Every job has its demands, and many people make sacrifices in their personal lives to advance their careers. However, actors and actresses sometimes experience some peculiar demands on their physical appearance, well beyond the common restrictions in other professions that may simply require neatly-trimmed hair of a natural color.
There are limitations to what can be done with stage makeup and padding. When performers make real changes to their physical appearance for a part, such that they look different in the mirror in the morning, that's commitment. That's Dyeing for Your Art.
This entry does not cover those actors and actresses who dye their hair all the time for professional or personal reasons e.g. Billie Piper, Gwen Stefani and the late Marilyn Monroe. They're Dye Hard. Though the two can overlap sometimes if an actor prefers the hair color they were required to change to and keeps it that way.
Often overlaps with Oscar Bait nowadays. When the casting directors opt to have the actors focus on their performance instead of the character's appearance it's Ability Over Appearance.
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Anna Faris is blonde, but dyed her hair black for the first two movies in the Scary Movie franchise as a parody of Neve Campbell in the Scream films. She gave up on it by the third, which is helped considering the main "inspiration" for that one, The Ring, also stars a blonde. She claims on Canned Ham: Scary Movie that she told the casting people she was a natural brunette. No doubt she knew what happens to blondes in horror movies.
Scream: Rose McGowan went blonde to play Tatum, to contrast with brunette Neve Campbell. Emma Roberts did the inverse for the fourth film, darkening her hair to play Jill, an Expy for Campbell's Sidney.
Bob Geldof actually shaved his own eyebrows off when playing Pink in the movie The Wall. However, he drew the line at shaving ALL of his hair off, so it looks like it's been simply slicked-back after his transformation.
Gene Hackman was tricked into shaving his mustache to play Lex Luthor in Superman. Director Richard Donner had had a mustache shortly before he went to see Hackman about the part. Hackman didn't know he had shaved it off already, so Donner wore a false mustache that the makeup department made up for him. When he saw Gene, he told him that if he shaved off his mustache then he would shave off his own. So, Gene Hackman shaved off his moustache right in front of Donner and then said "Your turn" whereupon Donner pulled off his fake. Hackman was most displeased but, fortunately for Richard Donner, is quite undisposed to violence. On the other hand, Hackman flat out refused to shave his head to play the famously bald Luthor. Instead, he came up with the Running Gag of Luthor wearing a different wig in every scene (and wearing a bald wig when he's arrested).
Gretchen Mol, a blonde, played the title role in The Notorious Bettie Page. Page was a brunette. Whether Mol dyed her hair or wore a wig on her head is not known, but in a couple of brief nude scenes, the hair in her lower regions was definitely brunette. You may draw your own conclusions.
Ingrid Bergman cut her hair quite short for her role in For Whom the Bell Tolls, annoying Max Steiner, who wanted her to come back and re-shoot some Casablanca scenes with an original song in place of "As Time Goes By".
Monica Bellucci, for the Italian movie Malena, dyed her own hair first red (and cut it at shoulder length), then blonde, then sacrificed it completely for the scene where she is shorn by force by the other women of the city. She went blonde again for the film Le Deuxieme Souffle.
For her role as a runaway teenage stripper in Welcome to the Rileys, she learned how to pole dance, deprived herself of sleep, chain-smoked, and ate mostly junk food. As a result her body and legs were covered with bruises, her skin was blemished, and she constantly looked tired.
Pauly Shore had his "trademark" dreadlocks shaved on-camera for In The Army Now.
Pete O'Hern grew a beard for the Peter Jackson film Bad Taste. Unfortunately for him, the film's low budget caused it to be filmed over four years, requiring him to keep the beard the whole time.
Rhiana Griffith shaved her head to play Jack in Pitch Black
Sofia Vassilieva (of Medium) shaved off her eyebrows and long blonde hair for her role as a cancer patient in My Sister's Keeper. Her co-star, Cameron Diaz, wore a bald cap for the brief scene where she shaved her head. Vassilieva reportedly got the role after Dakota Fanning stepped down, refusing to shave her head for the film.
Steve Carell's body-waxing scene in The 40-Year-Old Virgin was authentic. The results of the waxing are relevant to later scenes in the movie, so Carell had to have kept his chest hair in that condition for a while.
Telly Savalas shaved his head to play Pontius Pilate in The Greatest Story Ever Told — and it became a trademark for the rest of his career.
Tom Felton, for his role in the Harry Potter movies as the blond Draco Malfoy, bleached his hair for ten whole years. James & Oliver Phelps dye their hair red to be the Weasley twins, as did Mark Williams to play Mr. Weasley.
He had his infamously hairy body waxed/shaved for The World According To Garp, Hook, and Worlds Greatest Dad, to make him look younger in the first two cases, and as for the third, well, he was naked at the end. Old, fat, and naked is bad enough, we don't need hairy.
Yul Brynner shaved his head for The King and I, and (like Telly Savalas) didn't grow it back.
He also bulked up during The Ten Commandments because he didn't want to appear scrawny next to Charlton Heston....which is why he's so fit in The King and I.
Zachary Quinto shaved off most of his normally formidable eyebrows to play the role of Spock in Star Trek. Also, his Spock bowl-cut was real.
Ewan MacGregor actually grew his hair long so that the braid he wore as a Padawan would be his own hair, while the rest of the growth was shorn close, to play Obi-Wan. He also grew a beard for episodes 2 and 3.
Having your hair cut off is one thing but Vanessa Hudgens took this a step further by chopping of her own hair herself for the film Gimme Shelter.
Taylor Kitsch cut off his shoulder length hair in order to play a US Naval officer in the film Battleship.
There was a huge fan uproar when blonde Jennifer Lawrence and dark-haired Josh Hutcherson were cast to play the dark-haired Katniss and blonde Peeta in The Hunger Games. Director Gary Ross assured the fans that everyone would have the proper hair colors. Lawrence joked about it saying "I wasn't aware that everybody was so upset until after I got my hair dyed, and people were like, 'Oh my gosh, blond hair can turn brown. Wow. It's a miracle!' "
Works for horses, too. For The Black Stallion, the production team needed a solid black Arabian stallion. Instead, they found Cass Ole, who had a star and socks. Therefore, out came the dye.
One of the director/producers of Airplane! tells the story of being pretty much a punk kid at the time the movie was made, and hesitantly approaching Robert Stack and asking if just possibly the actor would be willing to dye his hair for the movie. Stack laughed and made a comment to the effect of "Don't worry about it, kid, when you bought me, you bought the package."
When Sadie Frost was cast as Lucy in Bram Stoker's Dracula she dyed her brown hair red because producers felt she resembled co-star Winona Ryder too much.
Emily Browning went platinum blonde to play Babydoll in Sucker Punch. The process ended up frying her hair and she had to cut it short the moment filming wrapped.
It took 36 hours for Nikki Reed (a natural brunette) to bleach her hair blonde to play Rosalie in Twilight. As a result she wore wigs for the remaining films. Ashley Greene wore a wigs for the first two films to play Alice but cut her hair short (firstly in New Moon to help it fit under the wig better) for the remaining films.
Franka Potente dyed her hair red for Run, Lola, Run. As the colour was so sensitive (and the entire film takes place over the course of twenty minutes) she couldn't wash her hair during production.
James McAvoy bleached his hair to play punk Rory O'Shea in the Irish film Inside Im Dancing.
Simon Woods who played Mr Bingley in 2005 version of Pride and Prejudice was asked to dye his hair ginger in order to match with his on-screen sister Miss Bingley (Kelly Reilly). The director said in the DVD commentary that Simon was slightly angry as the colour stuck and his hair continued to grow as such.
Andy Serkis, when he was cast to play Ian Dury in the biopic Sex and Drugs and Rock and Roll, spent time at the gym strengthening one side of his body so he could realistically emulate Dury, who had a crippled arm and leg as a result of suffering polio in his childhood.
Aishwarya Rai had to gain weight for her role in Guru. She then lost 22 pounds in three days for her role in Dhoom 2.
To the point where he actually had to lose weight mere days before shooting because the Thor tights were cutting off circulation.
Christian Bale already had to buff up a lot for his role in American Psycho. A few years later he lost 63 pounds to appear in The Machinist (2004), making him unhealthily underweight. (He actually shot for the exact weight of the character in the script, even as the director and the producers told him he was skinny enough. He was eating an apple and a can of tuna per day.) He then gained 40 pounds above his normal weight to play Batman in Batman Begins (2005), Then he lost 20 pounds of that. Later, he again became underweight to play an inmate in a Vietnam War prisoner camp in Rescue Dawn. Then he bulked up again to play Batman for the second time in The Dark Knight. Then he went skeletal again to play a crack addict in The Fighter (2010). Then he played Batman again in The Dark Knight Rises (2012). Let's just say Bale's refined Dyeing For Your Art to an art form itself.
Daniel Craig buffed up, gaining 20 lbs of muscle to play James Bond in Casino Royale. However, he did refuse to actually Dye For His Art for Bond. He wouldn't dye his blonde hair to fit better with earlier screen Bond's darker hair colors.
Donnie Wahlberg shed at least 25 pounds for his role as Vincent in The Sixth Sense, a character that was only on-screen for a couple of minutes early in the film.
50 Cent, known for his large physique, lost 55 lbs in 9 weeks by going on an all liquid diet and working out 3 hours a day in order to play a cancer stricken football star in Things Fall Apart.
Jared Leto resorted to fairly squicky methods (like drinking melted Haagen Dazs ice cream laced with olive oil and soy sauce) to gain the extra 62 pounds he needed to play John Lennon's killer Mark David Chapman in the film Chapter 27.
Jennifer Hudson gained 30 pounds to play Effie White in Dreamgirls. While Beyonce Knowles lost 20 pounds to play Deena in the same film.
Jennifer Jason Leigh got down to 86 pounds to play a girl suffering from an eating disorder in the 1981 telefilm The Best Little Girl in the World.
Karl Urban, while already a bulky actor, gained some more muscle to fit better under Judge Dredd's armor in Dredd.
According to Word of God , Laura Linney ate donuts and gained 20 pounds for her role in Kinsey. It's barely noticeable.
Mikael Persbrandt, a swedish actor, has lost more than 30 pounds and buffed up noticeably for his role as the title character in Hamilton.
Rain (Korean pop star) spent 8 hours a day in intense physical training, while eating nothing but salad and chicken, to play the lead in Ninja Assassin.
Richard E. Grant actually gained weight to match the script's description of Withnail in Withnail and I only to be told by the director that he had to lose a stone if he wanted the role.
Sylvester Stallone put on 40 pounds for his role in the movie Cop Land by eating pancakes at a local diner three times a day. By the time he was called back for reshoots he already lost the weight. He's also taken to using growth hormones to maintain his impossibly muscular physique for various roles.
Taylor Kitsch lost thirty pounds of muscle — and took up smoking! — to play suicidally-depressed photojournalist Kevin Carter in The Bang-Bang Club. Kidney problems resulted.
Thomas Jane trained with the Navy SEALs for about half a year and gained more than twenty pounds of muscle for his role in The Punisher 2004.
Val Kilmer needed to look sickly for his role as Doc Holliday in Tombstone, so he spent weeks leading up to the shoot eating almost nothing but onions and tomatoes.
Ditto for Dennis Quaid for the same role in the competing Kevin Costner vehicle Wyatt Earp. Quaid lost so much weight that he lacked the energy to stand and had to take frequent rests between takes.
Tilda Swinton gained a significant amount of weight for her role in Michael Clayton. She didn't seem to mind, though, as it meant she could basically eat everything she wanted until she met her target look.
Vincent D'Onofrio gained 70 pounds of fat to play Private Pyle in Full Metal Jacket. The added weight later caused the ligaments in his knees to tear up during the obstacle course scene.
300: the actors look like they're capable of incredible feats of strength and endurance. They were trained by a mountaineer named Mark Twight not just to look like that, but to be like that. They weren't just playing humans honed to Batman-like levels of physical might; they actually were humans honed to Batman-like levels of physical might.
Robert Downey, Jr. gained 20 pounds of muscle to play Tony Stark by adding weight training and significant diet changes to his usual Wing Chun training. Then he slimmed way down to play Sherlock Holmes, bulked back up to play Tony Stark again, slimmed back down to play Sherlock Holmes again, and bulked back up to play Tony Stark again.
The already quite fit Ryan Reynolds and Jessica Biel both went through extremely intense training for their action-intensive roles in Blade Trinity — working out 4 hours a day, 7 days a week, for several months.
Biel went on to lose a lot of that muscle mass, then gained a ton back for Total Recall (2012).
Anne Hathaway lost a significant amount of weight to play Fantine in Les Miserables (2012). She also did Fantine's Traumatic Haircut for real, on camera. . She refuses to say precisely what she did to lose weight, because she knows it wasn't safe and she didn't want to risk fans emulating her methods.
Hugh Jackman also lost weight, grew a beard, and went 36 hours without water for the opening scenes, after Valjean left prison. He then gained weight for the later scenes... and after filming wrapped had to bulk up to a return to his trademark role.
Charles Grodin has permanent scars on his wrists due to the handcuffs he wore in Midnight Run.
Charlize Theron put on about thirty pounds, partially shaved and bleached her eyebrows, and had her actual hair thinned and damaged to play serial killer Aileen Wuornos in Monster.
Choi Min-Sik, as the protagonist Oh Dae-Su in Old Boy, gained and lost considerable amounts of weight (repeatedly) to simulate a man being held in captivity for 15 years. Oh Dae-Su also kept track of how many years he had been confined by literally tattooing tally marks onto his arm. Unable to pull off the special effects required to depict this, Choi actually applied some of the tattoos for real on camera...using a piece of hot wire.
Ellen Page had her head shaved on camera for the film Mouth to Mouth, which led to her being mistaken for a boy when auditioning for Hard Candy. She nearly starved herself to look like (and feel the pain of) torture victim Sylvia Likens while filming An American Crime. A special feature on the Juno DVD shows her audition, and her face is so gaunt it's no wonder she had to gain back the weight in order to play a pregnant girl!
Demi Moore buzzed her hair down to the scalp on camera for G. I. Jane, and worked out religiously to simulate the effects of going through combat training. She had long black hair at the time.
Georgina Cates dyed her hair and pretended to be a natural redhead to win the lead in the film An Awfully Big Adventure. She also changed her name, invented a completely fake past from Liverpool (the same city as the character was from) and pretended to be a teenager when she was actually 21 so that the casting directors would see her for the role again - the first time she auditioned she was told she wasn't suitable.
Halle Berry didn't bathe and wore the same clothes for several days to convincingly play a crack addict in Jungle Fever.
Hilary Swank went into hard training, and put on twenty pounds of muscle, for her role as boxer Maggie Fitzgerald in Million Dollar Baby. She also cut her hair, lost weight, started binding (ie, flattening breasts) and generally acting like a boy for her role in Boys Don't Cry, to the point where her neighbours didn't recognise her and assumed that her brother must have been staying.
Jamie Foxx wore prosthetics over his eyes which made him blind for as many as 14 hours a day, and also learned Braille, in order to convincingly play Ray Charles in Ray.
He also starved himself for two weeks to play Steven Jay Russell, a con artist purportedly dying of AIDS. The real Stephen Jay Russel didn't have AIDS either, he merely starved himself and falsified his medical records as part of an elaborate escape plan. Carry also shaved off his widow's peak to expose more of his forehead and look smarter
He shaved his head (including his eyebrows) as well as his body for the "real world" scenes in The Matrix. Those scenes were the last ones filmed, and were shot all together. The very last scene shot was the one where he first woke up in the real world, and he had lost considerable weight to give a slightly emaciated appearance.
The producers of Speed demanded he have a more respectable haircut (he had long hair), but balked when he showed up with a buzzcut, trying to insist he wear a wig for the film. The Director vetoed.
She lost twenty pounds along with co-star Mila Kunis to play a ballet dancer in Black Swan, and took a year of ballet lessons before shooting began.
Nick Nolte grew out his hair and facial hair to achieve a crazed loner look for Hulk. It was in this unfortunate state that his infamous mug shot was taken. He also gained 50 pounds to play a paunchy detective in Q & A.
Peter Sellers' hair began to seriously gray in the late 1960s, so in many of his films from roughly 1969 onward, his hair is a dye job of some sort. A key exception is Being There, where he had his wife cut his gray hair short (figuring Louise, Chance's maid, would have been cutting it for him all these years). He also gained a good deal of weight, despite pre-existing heart problems, to reflect Chance's sedentary nature. Sellers was sensitive about his appearance and actually hated how he looked for the film, but felt it was what Chance should look like. (Some think losing the weight afterward contributed to his early death.)
Parker Posey had a dentist attach "train track" braces to her teeth to play a yuppie caricature in Best in Show. Michael Hitchcock as her character's husband settled for fake ones.
He famously gained 60 pounds to play Jake LaMotta in Raging Bull; he was one of the first actors to undergo such a transformation for an onscreen role. He gained the muscle training with the real Jake LaMotta until LaMotta decided he was ready to go pro - LaMotta later said that he thought DeNiro could have been in the Top 20 middleweights of all time.
He packed on thirty pounds and had his hairline shaved back and receded to play Al Capone in The Untouchables.
He also put on a little bit of weight for the scenes in The Godfather Part II where his character returns to Sicily.
For Cape Fear, he paid a dentist $20,000 to seriously screw up his teeth to play long-term prison inmate Max Cady. It cost him $25,000 to have the damage fixed after the movie was over. He was also tattooed with vegetable dyes, which fade after a few months, and worked out to the point of having almost no body fat.
Taxi Driver is a subversion, as he didn't really get his head shaved in a mohawk (they still had scenes to shoot with his hair, so a bald cap with a horse mane was put on De Niro's head). However, he did shed thirty-five pounds to play the role of Travis.
Russell Crowe gained weight and shaved his head to make room for a wig for The Insider, and gained lots of muscle for Gladiator.
British film critic Mark Kermode points out that Crowe does this for a lot of roles and claims you can identify Crowe's 'serious' films based on his paunch.
Tom Hanks grew a rather lengthy, unkempt beard and lost 30 pounds for Cast Away. He gained the weight he was expected to lose during filming in advance, and the movie was put on hold while he lost it. He also slimmed down drastically to play an AIDS patient in Philadelphia.
Tom Hiddleston dyed his naturally blond hair black (and straightened it) to play Loki in Thor, lightened it to a reddish-blond for Midnight in Paris, and darkened it again for The Deep Blue Sea. His poor, poor hair.
For Thor, Hiddleston had originally auditioned for the title role, gaining 20 pounds of muscle in the process. Director Kenneth Branagh then told him he'd be more suited for Loki, and asked him to lose the weight in order to play a slim, pale younger brother.
Robert Downey, Jr. did some pretty hefty physical training to bulk up for playing Tony Stark in the first one. In an interview, he said his logic was something along the lines of "I'm not going to be able to do this for too much longer, so I might as well while I can".
Kirsten Dunst wore a wig for the first movie, but dyed it for the second and third one.
Tobey Maguire had to gain some muscle to play Spider-Man. His worst experience was for the second movie, because he had become very thin to play a jockey in Seabiscuit.
Bryce Dallas Howard (Gwen Stacy) was the opposite of Dunst: redhead becoming blonde.
Spider-Man 3 scored the hat-trick of hairdyes when you factor in Elizabeth Banks as Betty Brant (blonde to brunette).
Topher Grace gained 24 pounds of muscle and bleached his hair to play Eddie Brock in Spider-Man 3.
Thomas Hayden Church put on 28 pounds of muscle and dropped 10 pounds of fat for Sandman.
Emma Stone is known as a redhead, but reverted back to her natural blonde to play Gwen Stacy in The Amazing Spider-Man - before her casting was officially announced, it was rumoured she'd be playing the red-headed Mary Jane Watson.
Super Troopers: all the members of Broken Lizard grew mustaches and built up their forearms to give themselves a more stereotypical highway patrolman look. One scene features Kevin Heffernan using one of the workout tools they used.
"I must admit I was starting to see a life free of steamed chicken breasts. They told me the idea and, at the time, it was Matthew Vaughn [directing]. Instantly, I knew it was a winner. It just felt like everything was coming full circle. However, I must admit my stomach and my mind were like, ‘Oh no.'"
To play Lisbeth Salander in David Fincher's remake of The Girl With The Dragon Tattoo, Rooney Mara chopped her long brown hair off and went to a dyed-black pixie cut, bleached her eyebrows, got both ears pierced four times, and got her eyebrow and one nipple pierced as well (lip and nose piercing was fake). Say what you will about her, she doesn't do things in half measures.
Noomi Rapace (the actress who played Salander in the original Swedish films) deserves mention also. In addition to performing image alteration similar to Mara's note she trained relentlessly to become thin and wiry, dyed and chopped her hair, got pierced (nopstril, septum, eyebrow and ear) etc., Rapace took up smoking for real during filming note smoking convincingly is actually quite difficult for non-smokers to emulate, and she wanted to get it perfect and took to dressing and acting "in-character" even when not on camera...to the point where family and friends began to worry as to her sanity. There's a very good reason she refused to do the role again for the American remake.
Averted in Once Upon a Time in the West. Henry Fonda, Cast Against Type as Frank, initally wanted to drastically change his usual appearance by growing a beard and wearing brown contacts. Sergio Leone told him not to do it, as the shock of seeing Fonda as such a character was exactly why he hired him, and it would work best if he looked like he usually did.
The whole cast of The Wizard of Oz had to suffer with long shooting schedules and the hot lights required for early Technicolor. But three in particularly were fit most for the trope due to heavy make-up: Margaret Hamilton (could not eat and remained on a liquid diet, the copper-based Wicked Witch make-up got burned by malfunctioning pyrotechnics), Bert Lahr (had the liquid diet before he decided to get his make-up redone everyday, the Cowardly Lion suit made of real lion skin made him sweat profusely) and Jack Haley (the Tin Man suit was so stiff that he had to lean against a board to rest; the make-up needed some changes as it previously caused the actor Haley replaced to get hospitalized).
For his Paganini movie, Klaus Kinski demanded from his dentist to pull all of Kinski's teeth, since the real Paganini had lost them. The dentist declined, since pulling perfectly healthy teeth isn't a dentist's job. Kinski reacted with one of his tantrums, but kept his teeth nonetheless.
Gangs of New York: trained as a butcher and learned knife-throwing. Sought out old voice recordings to get as close to a period-appropriate New York accent as possible.
For The Crucible, he built the house that John Proctor (his character) lived in in the film, and didn't shower or bathe at all during filming...and this was the film in which he met his wife, Rebecca Miller...
For Apocalypse NowMarlon Brando shaved his head to play Kurtz. To Coppola's chagrin, that's all he did to prepare for the part. He was supposed to lose weight for the role of Kurtz, but he showed up extremely obese.
To play Apple co-founder Steve Jobs in the 2013 biopic Jobs, Ashton Kutcher followed a fruitarian diet similar to the real Jobs. At one point, he ended up being hospitalized for abnormal pancreatic levels (which is particularly unnerving considering Jobs had died from pancreatic cancer).
Bruce Boxleitner grew a beard that he found very annoying for the last season of Babylon 5, at J. Michael Straczynski's insistence that his character be visually different to reflect his development.
Chloe Annett, The Other Darrin in the role of Kochanski on Red Dwarf, had her long light brown hair cut short and dyed dark brown so that she'd look more like her predecessor Clare Grogan when she took the role in Series VII. In Series VIII, she had her own natural hair (despite the fact that the series premiere took place a matter of minutes after the previous series' finale - the change in appearance was never commented on).
Daniel Roche, a child actor known for having long hair in sitcom Outnumbered, got a short back and sides to star in Just William.
Ed Bishop dyed his hair white-blond for the role of Commander Straker in UFO, as the character's look was based on a character voiced by Bishop in Captain Scarlet and the Mysterons, Captain Blue, but soon switched to a wig because the dye damaged his hair.
Eva Habermann dyed her hair blue to play Xev Bellringer on Lexx. Due to hair damage from the dye, she had to switch to a wig in the second season.
Gillian Anderson was asked to cut and dye her naturally long blonde hair into an auburn bob for the part of Dana Scully on The X-Files.
It was actually left long and blonde for the 2008 movie "I Want to Believe," which fit well with the character (who was supposed to be in hiding), but outraged fans at the change from the Scully they knew.
Groucho Marx never had a mustache most of his career; the comedic one he's always depicted with was a fairly obvious greasepaint job. When You Bet Your Life came along in his late career, he grew one so he could be at least partly recognizable.
Jason Lee grew Earl's trademark 'stache for My Name Is Earl, because he felt like the character needed one.
Alyson Hannigan dyed hers to add more red to it for her role as Willow. It's naturally red, but a bit more auburn than Willow's.
Kasey Rogers, the second actress to portray Louise Tate on Bewitched, originally dyed her red hair dark brown to more closely resemble Irene Vernon, the actress she replaced. In later episodes, she reverted to her natural hair color.
Leighton Meester, a natural blonde dyed her hair chestnut brown because Blair Waldorf is described as a brunette in the Gossip Girl books.
She actually dyed her hair before she even got the part, because people at the studio who didn't want her to be Blair kept using her hair color as a reason that she shouldn't be cast.
Linda Thorson joined The Avengers as a Suspiciously Similar Substitute for Emma Peel. She was supposed to dye her hair blonde to differentiate her from her predecessor, Diana Rigg. The treatment made her hair fall out, so in some early episodes she's wearing a brunette wig, while in others (e.g. "All Done With Mirrors") her hair is very short.
Mackenzie Crook, who played Gareth in The Office, said that he has his character's unflattering bowlcut in his wedding photos, captured for posterity.
Mike Lookinland, the auburn-haired child actor who played Bobby Brady on The Brady Bunch, was forced to dye his hair jet black to more closely resemble his TV father and brothers. In later seasons though, his natural color returned.
Mollie Sugden, who played Mrs Slocombe in Are You Being Served?, had to have brightly-coloured hair which changed colour every episode. At the start this was done by actually dyeing Sugden's hair, but the treatment caused reactions and hair loss so the production switched to a series of brightly-coloured wigs from then on.
Natalie Dormer is a natural blonde - she dyed her hair black to play Anne Boleyn on The Tudors.
Rose McGowan dyed her hair brown for a part as a brunette in Charmed but a potion blew up and she was a red-head again.
Sacha Baron Cohen's actual facial hair is used for Ali G and Borat.
Stephen Colbert had his head shaved to show solidarity for the troops when he took his show to Baghdad,note Hyping up having the President of the United States give the order to shave it, with said order being personally executed by Gen. Ray Odierno, commander of the American forces in Iraq at the time then made a Running Gag out of complaining about how slowly it was growing back.
Virginia Hey shaved her head and eyebrows to play Zhaan in Farscape. She was eventually forced to leave the show because the huge amounts of makeup were causing her serious skin and kidney issues.
Mark Strickson, to play Vislor Turlough, was required to dye his blond hair red. This was to avoid him being confused with the blond Peter Davison in long shots. This was a peculiar worry of the producer's, who also feared the audience would confuse Tegan (a twenty-something woman who normally wore a lilac air hostess uniform) and Adric (a teenage boy usually to be seen in a yellow and red pyjama-like costume). Well, they do both have brown hair.
Peter Davison had his hair highlighted to play the title role. This is particularly noticeable as it is considerably darker during his brief appearance at the end of Logopolis than it is in Castrovalva, despite the fact that the latter is supposed to follow on immediately after the former.
They must have loved this trope in The Eighties: Colin Baker was blonded up, too.
Louise Jameson wore brown contacts during her first season of playing Leela. At the end of Horror of Fang Rock, the first serial of her second season, an in-show reason was given to have have her eyes change from brown to blue (her natural color).
Honorable mention: When he auditioned, Paul McGann had a similar hairstyle to the one he has as the Eighth Doctor, but then he decided to shave his head. They made him wear a wig (which he absolutely hated) to get back the long curls, which had to be glued to his head, and his scalp had a reaction to the glue so his skin started flaking off. It's not an intentional example, but still, the poor guy's skin started coming off. It counts.note Amusingly, for nearly three weeks, Eric Roberts didn't recognize him when he took his wig off.
In the Granada Sherlock Holmes series, David Burke, the first Dr. Watson, dyed his grey hair and mustache auburn to make himself look much younger.
William Petersen kept his almost-white hair dyed darker to a gray shade for the later years of his role as Gil Grissom on CSI: Crime Scene Investigation. It does appear a bit more natural in his season 11 cameo, however.
Adrian Paul used hair extensions for the first season of Highlander: The Series and then grew it long for the next four. He cut it for season six because he was tired of caring for it.
Bridgit Mendler also has blonde hair as Teddy but showed an old school photo of herself in an episode with red hair, and complained about about not being able to get a suntan in another episode. That is a common complaint for redheads.
Pauley Perrette got a number of her NCIS character Abby Sciuto's tattoos done for real (but not all of them).
She already had a lot of tattoos. The spiderweb is not real.
Her hair has also been dyed from her natural blonde to the more well-known black - for the past seven years.
Summer Glau was accidentally hit in the face with a brass casing that left a small scar while training to handle weapons for The Sarah Connor Chronicles. Rather than have it removed by makeup, Summer instead kept it to help make the character of Cameron more convincing.
Tim McInnerny, in the fourth series of Blackadder, gave his character Darling an eye twitch that became a real tic over the repeated takes. He didn't lose it until months after the series ended.
Tom Fontana, series creator of the prison drama Oz, volunteered to be the man receiving an upper-arm tattoo of the show's logo. He even asked for the tattooing to be re-shot so as to get it perfect, but the tattoo artist refused, claiming if he applied the needle any longer, Fontana might die.
Tricia Helfer dyed her dirty blond-brown hair platinum to play Six on the reimagined Battlestar Galactica, but she switched to a wig a few episodes into the first season because the bleach was causing hair issues (namely, falling out in chunks), which explains how she was able to be both natural haired Gina and platinum Six.
In the same series, Edward James Olmos wore blue contact lenses and Jamie Bamber dyed his dark blond hair brown, so that they would look more like father and son.
Jamie Bamber dyes his hair brown for many of his roles.
Shea Whigham lost weight in between seasons of Boardwalk Empire to look appropriately gaunt after his character served 18 months in jail during a Time Skip.
Rob McElhenny (Mac) gained 50 lbs for the seventh season of It's Always Sunny in Philadelphia, and lost most of the weight as the season progressed. He has explained that making his character get fat was part of the sitcom deconstruction that the show is aiming for.
In addition to dying his hair, Benedict Cumberbatch also lost a lot of weight for the independent film Third Star instead of opting to shave his head. He kept it this way for Sherlock, which he justified by pointing out Sherlock almost never eats unless he has to, but regained a bit by the second series.
Michael Rooker lost 20 pounds to reprise his role as Merle Dixon on The Walking Dead.
Maisie Williams learned to swordfight with her left hand, despite being right-handed herself, in order to properly portray Arya Stark on Game of Thrones.
Enforced with the rather shameful example of castrati. Back in the earlier days of Opera, when prepubescent boys with good singing voices would be castrated so that their voices wouldn't break (and therefore ruin their ability to hit the high notes that composers were so fond of putting in their compositions). This practice eventually died out: castrati were frequently cast as women—which made sense in an age where few women took up acting or singing in operas, which was seen as unladylike somehow. When female opera singing became more socially acceptable, and stealing the manhoods of little boys was not, the practice gradually disappeared, and was finally banned in its primary center (Italy) in 1861 (shortly after unification).
The practice is also a bit of Fridge Horror when you consider that for many boys who underwent "the operation," other factors—ranging from the occasionally-lethal doses of opium administered to block the pain of the procedure to simple "your voice isn't good enough"—prevented them from actually singing upon reaching adulthood.
Till Lindemann got a hole pierced in his cheek so he could run a LED light through it for most of Rammstein's "Ich tu dir weh" video (It closed up during filming when he lost the plug keeping it open.).
Vocal fold operation is quite common for professional cante flamenco singers.
It's rumoured that some ballerinas will have their toes broken and reset to be better "en pointe," or to have their ribs removed to be thinner or change their body shapes.
Tina Turner famously fried her hair while dyeing it. She's worn wigs since the early 1960s.
Anytime someone loses a Hair-vs-Hair match.
Arguably the best example was Molly Holly. Originally during Wrestlemania XX, a Women's Championship match was not on the card. She decided that she needed to do something to get the Women's Title on Wrestlemania, so she offered her hair for it.
Molly did this more than anyone. When she initially debuted as Miss Madness in WCW she bleached her hair blonde and glammed herself up to look like a pageant queen. When her character underwent a Face-Heel Turn she darkened her hair to autumn brown and cut it (half symbolic to fit the new character, and half practical as her hair had been fried from years of bleaching). Then came the head shave...
For a while after he became the Hurricane, Shane Helms dyed a strip of hair on top of his head green. To get the green to stand out, he had to bleach his hair first. All the dyeing fried his hair and he had to stop.
Kurt Angle, after losing a Hair-vs-Hair match, wore a (bad) toupee for a while. In true heel fashion, he would freak out when someone pointed out it was a toupee. Once the toupee comedy ran its course, he debuted his bald look by whipping the toupee off and smiling until the fans quit heckling him.
For a good amount of time, Natalya Neidheart dyed her naturally blonde hair red, because there were too many blonde Divas in WWE. She's since gone back to her natural hair color, but with pink streaks as part of her new gimmick embracing her Hart heritage, whose signature colours were pink and black.
John Tenta had his LSU tiger tattoo changed to a shark to fit his new gimmick. Later as part of an angle he shaved one half his head bald, leaving the other half bearded and skulleted.
Jillian Hall felt she wanted to get breast implants when she was in OVW and Jim Cornette decided it would become her gimmick so she bleached her hair blonde as well and the storyline was that the implants leaked into her brain and turned her into a Dumb Blonde.
Roxxi Laveaux in TNA dyed her hair various colours to fit with her Voodoo Queen gimmick. The dye ended up stripping her hair which led to another example of the trope - where she infamously had her head shaved at the 2008 Sacrifice PPV.
Zack Ryder initially debuted in WWE with long red hair. When he was given his "Long Island Iced Z" gimmick, he cut his hair short and bleached it as well as tanning excessively to fit the character.
Serena Deeb had her head shaved bald on her Smackdown debut when she joined CM Punk and his Straight Edge Society. Reportedly, producers had gone around asking all the developmental Divas and Serena was the only one willing to have her head shaved. Punk himself later followed through on this and had his head shaved as a result of losing a match. Adding to the effect was the fact that the shaving had to happen while he had staples in his head from a cut during the match.
Madison Rayne went a few shades lighter to platinum blonde and gave herself black streaks when she joined The Beautiful People in TNA. When she switched characters to a Rich Bitch instead she dyed her hair brown.
Megan Hilty dyed her hair brown near the end of her Broadway run as Glinda in Wicked, and kept it through her run as Mary in The Musical of Vanities, but wore blonde wigs for both characters.
In We Will Rock You the Character of Scaramouche has Purple hair which is very obviously dyed from brown or black, the actress, depending on the production, may be asked to dye, or have their hair dyed purple for the role.
David Thaxton dyed his hair a lighter shade of blond when he was playing Enjolras in Les Misérables
At Halloween Horror Nights 2010, all of the actors in the Havoc: Dogs of War house were required to shave their heads to more accurately play genetically-altered super-soldiers, including the girls. This has led to some surprisingly good reviews of the house so far, despite being predicted as that year's flop, as the cast arguably consists of the most dedicated performers in the whole event. Some of them have gone slightly nuts in their performances and risked damaging sets.
Jermaine of Awkward. got his buzzed mohawk look to look authentically douchey. He had to keep it that way for two months.
Jodi Behan the titular bride in the famous viral video "Bride Has Massive Hair Wig-Out" did indeed cut off her hair for the video. She actually got the starring role because she was the only one of the four actresses willing to do so.
Referenced in-universe in The Simpsons. In one episode, Rainier Wolfcastle is seen coming out of a convenience store, grossly overweight and in the middle of gorging himself further. Wolfcastle informs his onlookers that he's preparing for a role as a fat secret agent.