For many modern cultures, the color pink has become the color meaning femininity, in all its forms. This means that the more feminine a woman is the likely she is to wear pink in fiction. It's also why it's thought girls appreciate pink things more than other colors.
The form of the pink is best done with elegant clothing (like the walls on her bedroom and the furniture), but even something "manly" being colored pink would count for this trope. Heck, even a dress that's not normally pink, like a Fairytale Wedding Dress, could be either colored pink (for being non-traditional, but still feminine), or have pink trimmings (usually in the form of a bouquet with pink flowers). A woman wearing sexy pink clothes can look naughty and nice at the same time.
This trope is Newer Than They Think. Pink is a shade of red, and red (being the color of blood) was considered masculine. Blue was the feminine hue (because it was associated with the Virgin Mary), and still is in some parts of the world.
The strong association of pink and a girly sort of womanhood makes this a delicate trope to navigate. For instance, a Tomboy will refuse to wear pink and her opposite, the Girly Girl, will insist on it. A favorite twist is to bring the "feminine and delicate" connotations into hard contrast with an Action Girl's rough, tough, and indelicate career. Expect the Girly Bruiser to wear pink while kicking ass. Real Men Wear Pink also plays on the contrast (often humorous) which comes up when a "manly" man is shown to enjoy "girly" pursuits.
By the way, this can include any shade of pink, even those that cross with other colors (like fuchsia, a purple and pink color). This is why the Graceful Ladies Like Purple trope exists.
A Sub-Trope of Tertiary Sexual Characteristics.
Played With throughout the Lyrical Nanoha franchise: the title character herself, a rather feminine young woman, has pink as the default color of her magic... which she usually uses to deliver a world of pain to her prospective friends and family. Then, we have Signum, a Lady of War who sports luscious waist-long pink hair... and is widely regarded as the manliest character in the series. Lastly, Caro Ru Lushe, whose hair and magic are pink... is a Girly Girl (and one of the most obviously heterosexual ones in this Les Yay-laden franchise, to boot), merrily playing this trope straight, even though she can summon dragons and huge dragons.
The title character usually wears red, white, blue, and yellow in her fuku, however her "aura" color appears to be pink, as whenever she's using an attack, pink is usually her main color. Her bow is also pink in the musicals and the live-action drama.
Sailor Chibi Moon's fuku always has pink, not to mention that her hair is pink.
Sailor Jupiter's dominant colour is light green but has pink for an accent colour, possibly since despite being the group's resident Tomboy she's also the most skilled at the traditionally feminine domestic arts like cooking.
It should be noted that in the case of Sailor Moon herself, pink does not necessarily mean feminine. Sure, there's a reason why she's caught some flak from groups that oppose stereotypical femininity, but compared to some other characters (Naru Osaka, Sailor Mercury, and Sailor Neptune come to mind) she's somewhat of a tomboy herself, a trait which was particularly alluded to in early seasons.
Ichigo Momomiya/Mew Ichigo, the leader of the Mew Mews from Tokyo Mew Mew.
Yeo Goseng and Yeo Miseng from Tower of God wear pink. Though the former is more a jaded snarker, Miseng is a typical little girl.
All of the chosen girls' Digimon have pink heavily featured in most of their forms. Sora's Yokomon and Biyomon are both pink all over though the Champion and Ultimate forms change to red/maroon. Mimi's Palmon has a pink flower for hair while her Ultimate form Lillymon is entirely pink, as is her Mega form Rosemon. Kari's Gatomon isn't pink in any of her early forms but Angewomon has a pink shawl and her Heaven's Charm attack creates a heavenly wave of pink energy. One of her Mega forms Magnadramon is also a pink dragon. Plus the crests of Love and Light (Sora's and Kari's) are represented by rose pink and pale pink respectively.
Sylia Stingray, the brilliant if flighty and eccentric leader of the Knight Sabers - whose day job is running a clothing outlet - uses this trope to humiliate her tomboyish singing biker teammate Priss Asagiri by forcing Priss to wear and be photographed wearing an ugly pink dress when Priss loses a bet with her, much to the amusement of everyone else (it made more sense in the original Japanese version than in the English dub). Naturally this came back to bite Sylia and the team in the ass when Sylia's ugly secrets came out, prompting Priss to tell Sylia and the team to go to Hell and leave them for a short spell.
Pink is a prominent color in Nene's hard suit. 2040 indicates that she and Linna have some pink unmentionables.
In the Gundam franchise, there are multiple examples of female pilots whose mobile suits have pink paintjobs and/or pink pilot suits. It's not true of every female pilot, but enough to be notable. Some of the notable examples of this include the Strike Rouge, whose suit takes on a pinkish hue when its Phase Shift armor is active, Lacus Clyne, who wears a pink flight suit, her replacement Meer Campbell, who is ferried around in a pink ZAKU Warrior and Kirara, who controls a pink Gerbera Tetra.
The girly outfit that Gwen forces Ben to wear in Ben's New Look.
Sharpay Evans of High School Musical is a drama queen and high school diva who wants everything to be fabulous which results in a lot of pink.
Legally Blonde: Elle wears pink to stand out from the rest of the crowd and to emphasise her femininity.
Mean Girls. The Plastics have these rules surrounding the color pink, which they must wear every Wednesday. Tomboy Janis owns nothing pink while Ambiguosly Gay Damian of course has a pink polo shirt.
In Suzie Q, Suzie wears a pink evening dress, and her mother comments that she finally got her daughter to wear fancy clothes. Possibly also an Actor Allusion, since in at least one film, Suzie Q was played by Amy Jo Johnson, a former Pink Power Ranger who (for a time) was quite annoyed by her time in pink.
Hermione Granger wore an airy pink dress (with a purple sash around the waist) to the Yule Ball in the film adaptation of Harry Potter and The Goblet of Fire. It's used to show her make a girl-into-woman Cinderella entrance fans were neither happy nor impressed).
Hermione again gets a pink dress, albeit of different design, for a brief Christmas Party gathering in the film adaptation of Harry Potter and the Half-Blood Prince.
Bond Girl Plenty O'Toole wore bright pink panties with light blue/purple lace when stripped of her purple dress in Diamonds Are Forever.
In The Sound of Music Marta enthusiastically says she wants a pink parasol for her birthday. Maria agrees and says that pink is her favourite colour too.
Subverted in the Vorkosigan Saga where the eight-foot-tall Cute Monster Girl, Sergeant Taura had been told that pink would make her look less intimidating. Because of this, most of her civilian wardrobe is a nearly fluorescent pink that does NOT work on her. One of the running gags in Winterfair Gifts is the efforts of the rest of the cast to correct her of this fallacy.
Delores Umbridge surrounds herself with pink, to try to cover up her Jerkass nature.
As well, when the Weasley twins open their shop in Diagon Alley, they have a range of items marketed to girls which are all pink.
April Devereux from Half Moon Investigations had a "Pink Club", which turned out to be a cover for a club determined to get girls a good education and will go to any measure to do so.
In Paranormalcy by Kiersten White, Action Girl protagonist Evie has a rhinestone-studded pink taser named Tasey, wears killer pink boots, and refuses to carry a knife until she is given one that is, you guessed it, pink.
A minor running gag in the Discworld books. Monstrous Regiment mentions that girls of around seven are magnetically attracted to the color pink, however they feel about it later. Brought up again in Making Money where Adora Belle Dearheart says that every girl of approximately eight years of age loves the color pink. This is used to rule out that the Cabinet of Curiosity at Unseen University could have been designed for a little girl, since it contains nothing pink.
The books of Angelina Ballerina, and its cartoon adaptations, put Angelina in a pink tutu.
Cindy, Chris and Cathy's very girly adopted daughter in the Dollanganger series, notes that "I love pink, really adore pink," and has a bathroom decorated in pink with gold and green accents.
Played with in Kaizoku Sentai Gokaiger. The gimmick of copying previous Rangers already mixes up the Gendered Outfit thing, but in the Gavan crossover movie, the entire team briefly uses pink Ranger Keys. However, it was ultra rare for someone not the Pink Ranger to wear pink. That all-pink morph may have been the first time.
Played with in Power Rangers Mystic Force, where Vida the Pink Ranger is about as un-feminine as you can get and was pissed at getting stuck with the pink suit with the pop-out butterfly wings. (This is a hilarious reversal of its parent sentai, too, where Magi Pink was Kawaiikosquared.) During Turbo / In Space, the more girly fashion-conscious Ashley is the Yellow Ranger, while the (slightly) more brash, tomboyish musician Cassie was Pink.
Averted in Time Force. Pink is Jen, a Badass with a vengeful streak and The Leader of the team (Red gets the usual standing-in-center priveleges because that's the rule, though.) There wasn't a Girly Girl that year at all. Yellow is a girl with Super Strength who loves to use it. However, Katie's more sentimental side comes out a lot more than Jen's.
Played with in Ressha Sentai Tokkyuger, where the Rangers are distinguished more by number than colour. They still have 'default' colours but can swap them around, including the default pink and red trading places.
In WWE the original Women's title had a pink strap on it, that the new FCW Divas' title also is modelled after. The current WWE Divas' Championship is also designed pink and the Divas' logo is pink. As far as I know the only diva who has not worn pink on her ring gear is Michelle McCool.
Mighty Molly (Molly Holly as the Hurricane's superhero sidekick) wore a pink and black outfit.
In a way Natalya Neidheart defied this trope whenever she wore pink as it was a reference to her Hart family lineage, whose colours are pink and black. So Nattie never comes across as feminine when she's seen wearing pink ring gear.
When they have to promote a Diva's match with a graphic, there's always some pink in the background and the text is normally pink as well.
Barbie has been wearing pink since at least the "Enchanted Evening" doll, and even has a copyrighted color of "Barbie Pink".
The body of the original toy release of Princess Celestia in the Hasbro toy line was pink colored and not white as in the show, apparently to appeal to little girls. It was however changed when the "bronies" complained.
Mass Effect introduces the character Ashley Williams in a pink uniform. Since it's a uniform, and Femshep doesn't wear pink, the color probably indicated unit affiliation rather than gender or fashion choice, and Ashley's lost unit all wore pink.
It could also be a manufacturer's mark, since all armour made by that particular manufacturer is in the same pink-and-white colour scheme.
Amy, the first playable female in the Sonic the Hedgehog series, doesn't wear pink. She is pink. Wherever possible she also incorporates pink into her vehicles and stage design.
The entire menu and user interface of Persona 3 is changed from blue to pink in the PSP version's female protagonist route.
Claire in the second Puppet Princess game, and Etoile's sprite in the first game.
Bad Girl of No More Heroes wears pink, but given her Badass nature, this seems to be just to keep up her Sweet Lolita image.
Vanille's pink top in Final Fantasy XIII. Serah, who also has pink hair also dresses almost entirely in pink, in nearly all her outfits save for the Mass Effect cosplay DLC and the Style and Steel cosplay, which are both black instead.
Flora, Professor Layton's adopted daughter, prefers this palette. She's first seen in a formal portrait, wearing a red velvet gown; later she wears a white dress with dark pink accents, and in the second and third games of the series she wears a peach-pink dress with dark pink or red accessories.
Almost every Star Fox character that's female so far has either worn pink, or is pink. Two didn't; Miyu and Fay from Star Fox 2 wore clothes just like the rest of Star Fox. However, their game was cancelled and they never got to see the light of day, so if they count is debatable.
In Inverloch, thief-catcher Lei'ella has daggers with pink hilts and matching belt. It's Lampshaded later when she replaces them with normal-looking ones; turns out her old boss and non-fiance-turned-stalker Berard had them made for her.
Neo Pets changed the Altador Cup team colours of Faerieland from pink and purple to green and purple/pink to symbolise the land's landing (it was airborne previously), but also to make it less of a "target group 5-year-girls" team.
Robert Mandell's best-known creations, Adventures of the Galaxy Rangers and Princess Gwenevere and the Jewel Riders, were distinct contrasts on this trope. In the first, Niko was only shoved into a pink dress once (while she and Doc were heading to a Bad-Guy Bar), protesting all the while. The latter cartoon was designed for a girl's toy line, and virtually everything was pastel, with the lead character rarely seen in any other color than pink.
Teryx, the only female Dinosaucer, has pink skin and darker-pink armour.
Inverted in HeyArnold. Helga's usual attire is a pink dress and bow, she writes poetry in pink books, and most of her clothes are either pink or white; however, she is easily the most tomboyish female character in the show.
Pre-Black Cat Felicia Hardy wore a pink skirt in the 90s animated Spider-Man series.
Megara from Hercules wears a light pink dress with a slit on the side with a dark pink sash around the waist.
Jean in the 90s X-Men had a few pink outfits, like a pink evening mini dress, and in the Fairy Tale episode, her fictionalPrincess counterpart wore purple and pink.
Averted with Pinkie Pie, the pinkest pony of the main cast, who isn't particularly girly.
Played straight with Fluttershy, who is very feminine and has a pink mane and tail, as well as a partially pink cutie mark.
Proper pink princess Cadance... who is nonetheless badass enough to singlehandedly defend her kingdom for weeks without sleep, and with assistance from her husband sent an enemy army flying over the horizon. Studio B likes to play with tropes, can you guess?
Played straight with the males. Although there are mares of every single color imaginable, there has yet to be a pink stallion.
In Sleeping Beauty Flora and Merriweather row over what colour Aurora's dress is to be. Naturally the more feminine Flora insists that it must be pink, though the dress spends most of the film blue.
Played straight for Flora in Winx Club, she is very feminine and many of her fairy forms are primarily pink.
Mary Kay Cosmetics frequently rewards its top salespersons with pink cars. The Mary Kay/pink association was lampshaded in a Bloom County arc where Opus tries to locate his mother among the test animals at Mary Kay's cosmetics labs, only to be cornered by the Mary Kay Commandoes; "Even their Uzis are pink!"
Before the forties it was Inverted with pink being a boy's color and blue being a girl's color.
‘Pink’ is sometimes used as a slang term for, ahem, a certain part of the female anatomy.