Snow White and the Seven Dwarfs has Snow White (blue) and the evil queen (red). Snow White is very sweet, kind to animals and other people, and naïve while the evil queen is jealous, tyrannical, abusive, vain, arrogant, and murderous as she is obsessed with killing Snow White so the queen could become the fairest of the land.
Any of the seven dwarfs can qualify but Grumpy is seen as red and Dopey as blue. Grumpy is most angry, reckless, impulsive, and very loud while Dopey is soft spoken, sensitive, silent, and happy go lucky. Grumpy also wears red clothing while Dopey wears green clothing and a purple hat.
Genie and Carpet from Aladdin. Energetic and boisterous Genie is the red to Carpet's blue.
The Lion King: Mufasa (blue) and Scar (red), who are brothers. Mufasa is more kind, caring, and rules the pride lands with a benevolent desire to help others while Scar is jealous, arrogant, self centered, and very sneaky. After Mufasa's death, his son, Simba replaces his father as the blue Oni.
Timon (red) and Pumbaa (blue). Its not very evident in the film but is more present in their own series and later films. Timon is sarcastic, self centered, reckless, and has a more impulsive temper while Pumbaa is more sensitive, kind, caring, cautious, and has a more controlled temper.
Lilo & Stitch: Lilo (red) and Nani (blue). They are both sisters, which helps this trope. Lilo is more adventurous, outgoing, and more reckless while Nani is more cautious, strict, and very protective of Lilo. Also Lilo wears a red muumuu while Nani wears a light blue shirt.
Though Lilo can be seen as the blue, to Stitch's red thus reverting this trope once more.
Aliens Jumba (red) and Pleakley (blue). Jumba is more reckless, masculine, impulsive, and would take aggressive approaches to completing tasks while Pleakley is more laid back, sensitive, effeminate, and cautious towards finishing tasks.
Although its not evident in the first film, Gantu (red) is paired up with Reuben "Experiment 625" (blue). Gantu is very aggressive, impulsive, reckless, and would go through violent and extreme means in capturing experiments while Reuben is more sensitive, laid back, lazy, and more focused on making sandwiches than capturing experiments. Ironically, Gantu's skin color is bluish-gray while Reuben's fur color is yellow.
Charlotte and Tiana. They also fit the Tomboy and Girly Girl mold as well, with Charlotte being the loud, over-dramatic, ditzy, Spoiled Sweet dreamer and Tiana being the quieter, more down-to-earth working girl. Also, one scene has Charlotte in a pink ballgown with Tiana in a (borrowed) blue dress.
Tiana and Prince Naveen also fit the description to a T, with Tiana being a serious Workaholic and Naveen being overly laid back and lazy.
Louis the alligator (blue) and Ray the firefly (red). Ray is more crude, sarcastic, and often charges into a fight while Louis is more laid back, sensitive, and is afraid of guns.
The Distant Duet "The Plagues" has Moses in orange light and Ramses in blue shadows at the end of the song. Their clothing choices throughout the film follow the same color scheme. It fits their overall personalities as well, with Moses being the impulsive and exuberant one that gets them both into trouble, and Rameses being the overly thoughtful, in-control type hailed as a great leader. (Though ultimately, Moses’s passionate nature results in empathy and compassion and enables him to save his people; whereas Rameses’s analytical, rule-following stoicism makes him cold and ruthless and causes his greatest fear—ruining his father’s legacy—to come to pass.)
Moses' siblings, Aaron and Miriam, are a good beta example of this trope: Aaron is cautious and comes off as cold and uncaring while Miriam is passionate, warm and impulsive. Like many other pairs, their clothes are a reflection of this.
North and Bunny who are also Colour-Coded for Your Convenience, the former wears a red coat and is boisterous and loud, while the latter has bluish grey fur and is more stoic and meticulous.
The chatty and flighty Tooth (red) and the quiet and laid-back Sandy (blue).
Jack is the mischievous, fun-loving and impulsive hero (red), and Pitch is the cold, cunning and suave villain (blue).
Rapunzel and Flynn from Tangled. Rapunzel is an energetic, innocent, stubborn and emotional dreamer and Flynn is a laid-back, snarky, somewhat grumpy and jaded criminal. Appropriately, Rapunzel wears a pink dress and Flynn wears a blue vest.
Judy is energetic, naive and impulsive while Nick is laid-back, cynical and cool-headed. In a touch of irony, their colors are reversed as Judy wears a blue police uniform and Nick has red fur.
Chief Bogo is hot headed, strict, muscular, and more masculine while Benjamin Clawhauser is more laid back, sensitive, compassionate and effeminate
Film - Live Action
The Back to the Future movies have Marty McFly and Dr. Emmett "Doc" Brown. In Part I, he also played red oni to his father George's blue oni in 1955.
A villainous example in Big Game: the Big Bad Duumvirate has hot-headed, always furious Morris as Red and cold, detached, psychopathic Hazar as Blue.
The two detectives at the center of The Black Dahlia are referred to explicitly as Mr Fire (red) and Mr Ice (Blue).
The Will Ferrell movie Blades of Glory has Chazz Michael Michaels, the improvisational, womanizing idiot Red Oni, and Jimmy Macelroy, the technical, thoughtful man-child Blue Oni. This is even reflected in their "Fire and Ice" costume.
In Blonde in Black Leather, Claudia starts out as idealistic and naive, with Monica passing for cool and street-smart (they're also dressed in the respective colors). They switch roles as the movie goes on, with Claudia becoming savvier and more down-to-earth while Monica comes off as something of a manic-depressive.
Every Die Hard movie has one or more elements of this. John McClane, the hot headed runner and gunner always goes up against a calculating intellectual Big Bad. The first two movies also have a subplot involving McClane's "Red Oni" tactics budging up against the "Blue Oni" by-the-book style of the authority.
The plot of Tokyo Drift can be summed up as "Two Red Onis fight, everyone else is a Blue Oni trying to stop them". That said, Sean does play a good Blue Oni to the impassioned, arrogant Red Oni DK.
In the main timeline, Brian is the confident, out-there Red Oni running circles of fire around the careful, controlled Blue Oni Dom. This only describes their usual demeanors, however - Brian has his Blue moments from his former career in law enforcement, Dom can easily out-Red Brian with an angry and brutal No-Holds-Barred Beatdown whenever someone gets under his skin.
The title character (sloppy, hot-tempered demon dating a human flamethrower) and Abe Sapien (studious, slightly prissy gillman) are actually addressed as "Red" and "Blue" respectively; although this is due to, y'know, their actual skin color, the association still fits.
Hellboy and Kraussin Hellboy II: The Golden Army, particularly when Krauss is possessing that Golden Army trooper in the final scene - all his glowy bits go blue. They fit the personality portions of this trope to a T.
In Raiders of the Lost Ark, Belloq is the blue oni to Indy's red oni. This ties into their preferred methods for acquiring artifacts. Indy is hands-on and collects them personally. Belloq hires other people to do the dirty work while he stands off to the side acting sophisticated.
In the movie version of L.A. Confidential, Edmund Exley is a near-perfect example of a blue oni (and nearly always dresses in a blue suit to boot), while Bud White is very much a red oni (complete with brown/maroon suit).
Laurel and Hardy: Usually, the harsh and boisterous Ollie is the red one, while the calm and submissive Stan is the blue one.
Maiko Haaaan!!! combines this with the traditional kabuki hero/villain colour schemes. The protagonist, Onizuka Kimihiko, is very excitable and is driven by his passions while the antagonist, Kiichiro Naito, is much more reserved and collected. Unless he's drunk.
The Man from U.N.C.L.E. (2015) has Napoleon Solo as the Blue Oni (a suave and analytical CIA operative) and Illya Kuryakin and the Red Oni (a hot-blooded KGB agent who often seems to be only just keeping his emotions in check). This is particularly noteworthy because it is an inversion of their Oni roles in the original series on which the movie was based where Napoleon was the comparatively cheerful and easygoing American and Illya the coolly intellectual Russian.
Thor and Loki in all of their appearances are the epitome of this trope. Although, given their colour schemes, it's more like Red Oni, Green Oni. Though Loki does wear blue in Ragnarok.
Another example would be Iron Man & Captain America. The brash and arrogant antics of the red-clad Iron Man really don't sit too well with the humble-natured and calm Captain America, who wears blue.
In the regular Iron Man films, James Rhodes is the blue Oni to Tony's red. And, like Rogers, he is usually seen wearing blue.
Another member of the Avengers who embodies both Onis is mild-mannered scientist Bruce Banner and his alter-ego the Hulk, who is literally a raging id.
The two major Superhero Teams in the MCU (The Guardians of the Galaxy and the Avengers) can qualify as a Red Oni, Blue Oni dynamic. The Guardians are very cavalier and disorganized, while the Avengers are very orderly and mindful.
In Men in Black, Agent K is the serious, deadpan blue oni mentor while Agent J is the wisecracking, impulsive red oni rookie.
Osmosis Jones has this with a color inversion. Ozzy is the Red Oni and Drix is the Blue Oni. This is despite Ozzy being blue and Drix being red.
In Pacific Rim, Newt and Gottlieb are red and blue respectively.
The Phantom of the Opera: Christine herself is both Oni colours considering she's both an amazing singer but understanding others as well. The Phantom is the Red Oni, who displays much lust, flare and has the most dramatic roles in the story. Raoul is the Blue Oni opposite to the Phantom, for he protects Christine without being obsessive or threatening.
La Carlotta and Christine form this dynamic as well, in both personality and singing style.
Pulp Fictionzig zags this trope with Jules and Vincent. On the surface, the former is hotheaded and the latter is calmer, if not outright aloof. As the film progresses, it's quite clear that Jules is the one with the more level head and that his "Bad Motherfucker" tendencies appear only when someone (usually Vincent) says or does something really stupid. Vincent, on the other hand, is a bumbler, needlessly starting a brief argument with the Wolf when presented with advice to solve a problem he started and leaving dangerous stuff around for people to find (Mia with the drugs, Butch with the sub-machine gun) .
RedTails: The primary character conflict is between Hero/Lancer duo Easy and Lightning. Blue and Red respectively.
In Rush2013, the hardcharging partyboy James Hunt is the red oni to his rival Niki Lauda's cool, cerebral blue oni.
Professor George Falconer (blue) and his student Kenny Potter (red) from A Single Man. They even somewhat acknowledge/discuss this trope when Kenny buys a red pencil sharpener for himself and a yellow one George picked out for George. Kenny shows surprise George didn't pick blue. All of George's relationships fit this mould, actually, and there's some hints Kenny's best friend is also a blue to his red.
The Sister Act films have an interesting example of Red Oni, Blue Oni pairs. Deloris/Sister Mary Clarence and Sister Mary Patrick are Reds. Sister Mary Lazarus and Sister Mary Robert are Blues.
The Sith and the Jedi fits this trope to a T. The Sith wield red lightsabers and are defined by their passions and their ambitions. While the Jedi typically wield blue or green lightsabers and are presented as more intellectual and steeped in tradition.
On a more individual level, the master/apprentice relationship between Obi-Wan Kenobi and Anakin Skywalker during the prequel trilogy. Obi-Wan is the more cautious and thoughtful blue Jedi and Anakin, being younger and more ambitious, represents the passionate red. Of course, this speaks volumes about the paths the men choose by the end of the end of said trilogy.
Later (or earlier, depending on how you look at it), the trope is played with by Han and Luke. They switch roles as Character Development ensues: Luke starts out as the impulsive idealist to Han's world-weary cynic, while by the third film Luke is the disciplined and determined warrior and Han is the emotionally driven one.
Franchise-wise, the prequel trilogy is the red oni to the original trilogy's blue oni.
The iconic factions can be seen this way: The Rebel Alliance were the unprepared, unethical, luck-relying red oni to the militarized, orderly, and prim blue oni, Galactic Empire.
The same for the Clone Wars, The Separatist Droid Army were the red oni to the Galactic Republic's Clone Army blue oni.
R2-D2 and C-3PO can qualify. Artoo is very impulsive and reckless, while Threepio is very cautious and timid. Ironically, Artoo has a blue and white color scheme, while Threepio has a gold color scheme but does get a red arm in The Force Awakens.
Finn plays the Blue Oni to Poe Dameron's Red, and afterwards, the Red Oni to Rey's Blue Oni.
Among the villains from The First Order, Kylo Ren, the emotionally unstable Dark Side enforcer, plays Red Oni to General Hux's Blue Oni, who has better control over his emotions despite being impulsive himself.
Among the current Sith, Kylo Ren as usual remains the desperate and pleading Red Oni to his master Supreme Leader Snoke's calm and calculating Blue Oni, who only got frustrated once during the entire film.