An (almost) literal contrast in 80's animated film Transformers The Movie: Hot Rod, impulsive and flame-themed (well, his name is a hint), is red (in a color tone tending a bit to magenta). Kup, calmer and more experient, is greyish blue (or blueish gray).
Also in Transformers' eyes. The wild, violent Decepticon have red eyes; The good-hearted, rigtheous Autobots have blue eyes.
Teen Titans has two sets: Robin and Starfire are represented by Red and are more brash, stubborn, and passionate than the others (Starfire displays this most in the comics, to which the flashback/origin episode "Go" paid tribute). Cyborg and Raven are represented by Blue and are more intelligent, analytical, and, in Raven's case, cold.
That, when they are in combat, but when they just hang along, Starfire and Beast Boy are more on the Red side, due to the fact that they are almost always happy, laid-back, and carefree, while Raven and Robin have blue traits, being controlled, calm, and down to earth. Cyborg falls in the middle.
In the current Teen Titans comic, Red Devil (literally a Red Oni) and the new Blue Beetle have become a comic relief dynamic duo that fans have dubbed Beevil. While both characters have similar personalities, Beetle tends to be level headed while Devil is more impulsive.
Don't forget about Thunder (blue) and Lightning (red).
Slade is definitely the villainous Blue to Robin's heroic Red.
Avatar The Last Airbender has played with the red vs. blue color game quite a bit. Probably the most clear cut case for this in actual characters is the contrast of angry, defiant Determinator Zuko, who lives and dies with the Indy Ploy (although he is by far one of most complex reds), and the Dangerously Genre SavvyChessmaster/Dragon Azula, who even makes blue fire (which is actually hotter). Some other notable examples of playing with red vs blue include:
Best friends turned enemies Avatar Roku and Firelord Sozin both had dragon companions. Roku's was red, Sozin's blue. Sozin tricks Roku, leaving him to his death.
Zuko also plays Red Oni to every one of Team Avatar's Blue Oni's (except for Toph).
Aang and Zuko are taught a different version of Firebending philosophy, formed, at least in part, by a red and blue dragon. Zuko is being taught to move beyond destructive motivations (his red oni background) while Aang is being taught to accept his destructive potential (against his blue oni background). Also the contrast in their facial markings. Zuko's Red Scar and Aang's Blue Tattoos.
Zuko and Katara in general Zuko is angry and passionate while Katara is caring and nurturing, however in the interactions between just the two of them, they switch roles. Katara is constantly angry and emotional and extremely protective of Aang and her own interests. Zuko is calm and thinks about how to deal with her. Katara is typically dressed in blue and Zuko in red.
Except, of course, in each of their 'spirit' alter-egoes: the Blue Spirit and Katara's reddish Painted Lady. In that commonality, their color schemes reverse.
During the Boiling Rock infiltration Sokka was the Blue Oni, A non bender Water Tribesmen strategist and The Leader vs Zuko's Red, a Firebending Fire Nation fighter and The Lancer.
Aang is, appropriately enough, a combination of the two. Aang normally can be both foolish and passionate (represented by his normal saffron clothes and temporary Fire Nation wardrobe change, which he later salvages to make a new set of robes). But when in his glowing blue Avatar State, Aang can become frighteningly cold and ruthless, to the point where Aang himself has nightmares about it.
More broadly, this applies to the Fire Nation and Water Tribe. Fire Nation are typically dressed in red (and black) compared to the Water Tribe, who are typically dressed in blue (and white or gray). Firebeinding is offensive, Waterbending is mostly defensive.
And The Fire Nation and the Southern Water Tribe first families have a Missing Mom, a child prodigy 14 year old daughter and a less skilled 16 year old son who wants to make his father proud. The difference is that the Fire Nation is dysfuntional and brutal, while the Southern Water Tribe family is supporting and caring.
The Siege of the North - the Fire Nation troops are the aggressive attackers whose deluded military leaders (General Zhao and Prince Zuko) are busy with insane schemes (to kill the Moon spirit and capture the avatar respectively). Meanwhile, the Northern Water Tribe are defending themselves, planning to infiltrate the Fire Nation navy]] and seek help from the spirit world. The color scheme throughout those episodes fits this trope to a t - the moon and night sky become blood red when the Fire Nation Admiral Zhao begins to kill the Moon Spirit, foolishly risking the destruction of the earth in order to prevent water benders from bending, thereby making the city an easy target. The response from the Northern Water Tribe is exceptionally non-aggressive, as the princess, something of an incarnate of the Moon Spirit, sacrifices her mortal life with the aim of restoring balance to the world and enabling others to fight against Fire Nation imperialism.
Also, the (red) Fire Nation and the (green, not blue) Earth Kingdom during the attacks and sieges of Ba Sing Se and the establishment of Fire Nation colonies, where the Fire Nation are pretty clearly the (unsustainably) aggressive party. Of course, the Earth Kingdom has the Dai Li, who dress in cooler colors and engage in more underhanded aggression, like brainwashing.
Although, at first, Stan and Kyle from South Park had similar personalities, later on, they were differenced. Stan was an introvert, calm Deadpan Snarker, while Kyle was an impulsive, bold Hot BloodedSnark Knight, especially in Cartman's presence.
Tweek and Craig fit this trope, as well. The former is hyperactive, paranoiac and anxious, who shows his emotions easily, while the latter has a darker personality, being stoic, pragmatic, monotonic, and ironic.
Possibly unintentional, but Blitzwing of Transformers Animated has a Split Personality represented by his three faces. The black face is The Mad Hatter, but the red and blue faces are textbook red and blue oni: the blue face is cold, calm, and calculating (and uses ice powers), while the red face is brash, impatient, and agressive (and uses a flamethrower).
Even his alternate modes reflect this; the blue face wanted to choose a fighter jet, maneuverable and good for attacking from a distance, while the red face insisted on an assault tank, heavily armored and bristling with firepower, ideal for being right in the middle of the action. After they'd argued for a bit, the crazy face stepped in and, cackling madly, scanned both; which one he uses depends on which of him is driving.
Interestingly, while you'd expect Jetfire and Jetstorm to follow the trope (they even have red and blue color schemes, respectively), they avert the trope by both acting pretty red. Of course, they are working for Sentinel Prime, so who knows how that affects their personalities.
Sentinel Prime is the red who is reckless and an arrogant jerk, Optimus Prime is blue, being far more level-headed and humble to everyone. Ironically, Sentinel's primary color is blue, while Optimus' is red.
Then there's Bumblebee, who's Hot Blooded, and Prowl, who is more mature and more experience in fighting.
SWAT Kats: Chance 'T-Bone' Furlong and Jake 'Razor' Clawson. And when they're seen outside their vigilante and work clothes, they're wearing their respective colors.
In fact, they pretty much summed up the trope in four words with this exchange from the first episode of the '03 series:
Raph: Teacher's pet!
Leo: Ninja dropout!
Even the other two turtles, Donatello & Michelangelo, fit this trope. Michelangelo being the wild, extroverted, and more emotional Red to Donatello's calm, introverted, and more logical Blue.
Inverted with Pablo and Tyrone of The Backyardigans: Pablo's blue, hot headed, and panicked a lot in season 1, placing him as the Red Oni. Orange-furred Tyrone, on the other hand, is calmer and more level-headed, which are true aspects of a Blue Oni.
In the cartoons series for Disney's Hercules, Ares the God of war and Athena the Goddess of wisdom, who were siblings and rivals, were perfect representations of this trope.
The crossover between Aladdin has Jafar and Hades under these with their colors.
Aladdin the Animated Series: Aladdin: red/purple and white, uses his own strength, lives with a mess of friends, has a monkey sidekick, versus Mozenrath: dark blue and black, uses magic, lives pretty much alone in a ghost city, has an eel sidekick.
In Taz-Mania the Taz/Dingo shorts, Taz plays the role of the Hot Blooded red oni while Digeri Dingo plays the role of the cool and cunning blue oni. Also, Molly and Jake, with Molly being the easily-stressed red and Jake being the more cheerful blue.
In Bonkers, Bonkers (red) and detectives Lucky Piquel and Miranda (blue).
In Invader Zim, Gir seems to show some signs of this trope, though the colors are reversed. The first few seconds when he was active, the episode "Gir goes Crazy and Stuff", and occasionally through-out the series, Gir's colors switch from blue to red and back again. When red, he seems to show the traits of the Blue oni and is intelligent, calm, and eager to serve his master (often saying "Yes my Master!"). When Blue, he acts more like the Red Oni and is wild and over the top, with no control over his own urges or actions.
There is also the scene were Zim hypnotises Dib and the scene shows the ground falling apart with Zim in red and Dib in blue. Makes sense, since Zim is known for being impulsive and not thinking before acting, where as Dib is more scientific and logical (if only by a little bit).
Dagget (red oni) from Angry Beavers is highly emotional and prone to Donald Duck-esque rages; stark contrast to his older brother, Norbert (blue oni), who is cool-headed and considers himself suave.
Trevor and Aeon from Ćon Flux. Subverted, in that Aeon, despite being a cool, calculating, cause-oriented Blue Oni, is meant to represent chaos and anarchy, whereas Trevor, the vain, arrogant, people-oriented Red Oni, represents order and stability.
Out of the stretchy superheroes in Batman The Brave and the Bold, Plastic Man, who wears red, is much more blunt and okay with stealing valuables from the scene of the crime, while Elongated Man, who wears purple (it's a kind of blue) is much more analytical and noble. Plas has a similar dynamic with Batman himself.
Likewise, Batman (Blue) and Aquaman (Red), Atom (Blue) and Aquaman (Red), heck, anyone and Aquaman.
In Titan Maximum, the original Titan Force Five had the Hot Blooded Palmer and his Lancer Gibbs (they even wear red and blue respectively). However, the fact that Gibbs was the Only Sane Man of the team (as well as Palmer leaving him to die just so he wouldn't miss a hot date) led to Gibbs turning evil in the first episode.
Tiana and Prince Naveen also fit the description to a T, with Tiana being a Work-A-Holic and Naveen being overly laid back and lazy.
The Amazing Chan and the Chan Clan has two examples, one with an inversion in color: sweet-tempered Suzie wears blue while boisterous tomboy Anne has a lot of orange in her outfit, but responsible Henry wears orange while impulsive goofball Stanley wears blue and green.
One episode ("Alter Ego") of the 1970's era Filmation Sabrina, Superwitch cartoon featured Damina, a raven-haired Sabrina lookalike with a shrill, grating voice. Depending on who you ask, Damina is Sabrina's "magical mirror image," Sabrina's alter ego, or merely Sabrina's cousin, but what is clear is that she and Sabrina are literal examples of the trope; the rowdy and rambunctious Damina wore a red dress, and the demure and proper Sabrina wore a blue dress.
Henry and June in Ka Blam!: Henry is the red oni (he's energetic, idiotic (not to extreme levels)), while June is the blue oni (cool, cynical, smart). With June, it kind of makes some sense: she does have blue hair, after all.
Ironically, Henry wears a blue shirt, where as June wears a red jacket.
In Life with Loopy, Loopy is the red oni (energetic, life-loving) to her older brother Larry's blue oni (inteligent, shy). Oddly enough, the colors of their hair are the opposite (Loopy has blue hair, Larry has red).
The Mooninites from Aqua Teen Hunger Force. While they are both still immature jerks, Ignignot is much more level-headed and sarcastic than the vulgar, in-your-face Err.
Beavis And Butthead are a borderline case. While both of the boys are active pranksters and neither of them show good judgement, Beavis is Hot Blooded, brash, irritable, and violent, while Butthead is more laid-back, calmer, and (barely) smarter. Ironically, Beavis wears a blue shirt while Butthead wears red shorts.
Wakfu has this dynamic between Amalia and Evangeline. Amalia is a Rebellious Princess who absconds for little reason other than boredom and brattiness. Meanwhile, Evangeline starts as a stoicTyke Bomb with Undying Loyalty to the Sadida royal family. She is all about duty and self denial and doing what's right. But as things go on, they both learn from each other and end up reaching more balanced positions on the matter of responsibility. Amalia learns from the example of Evangeline's courage and commitment, taking up the challenge of living up to her royal responsibilities and defending the Sadida kingdom at its darkest hour. Evangeline, at the same time, learns how to enjoy herself without compromising her duty.
Freakazoid and Cosgrove in Freakazoid. In the episode "Two Against Freak", RoddyMacStew fills in as the Red Oni while Freakazoid is in the hospital. They're even - albeit unintentionally - in the right colors: Freakazoid's in red tights and Roddy's kilt is red, while Cosgrove is always in his blue police uniform.
Used a bit with the main six in Recess when broken into three groups of two:
T.J. as the red oni (hot-headed, easily excitable) with Vince as the blue oni (cool, sarcastic)
Spinelli as the red oni (hot-tempered, tough) with Gretchen as the blue oni (smart, laid back)
Mikey as the red oni (outgoing, drama king) with Gus as the blue oni (shy, quiet)
Legend Of The Dragon has the dragon twins Ling and Ang. You may think from looking at pictures that Ling is the blue Oni and Ang is the red Oni. However, in terms of personalities, Ling is the red Oni and Ang is the blue Oni.
Foster's Home for Imaginary Friends: Bloo (red oni) is obnoxious, self-centered, and rude, while Mac (blue oni) is intelligent, shy, and always wants to do the right thing (most of the time). Ironically, Bloo is well, blue, while Mac wears a red t-shirt.
The Revenge Couple on Total Drama, Trent and Courtney. Courtney is a red oni and Trent is a blue oni.
Another couple, Gwuncan, also fits for this trope, as Duncan is a red oni, while Gwen is a blue oni.
Outside of battle, red-clad Iron Man often acts more brash and short-tempered than the calm, reflective, and blue-clad Captain America.
For most of the first season, The Wasp loves the exciting and beneficial qualities of crimefighting, but her colleague, Ant-Man (whose red costume seems ironic in this case), prefers to confront criminals by talking things out and rehabilitating them. They switch roles during scientific projects, which Ant-Man enjoys more than Wasp does.
One of Wasp's friends, red-clad Ms. Marvel, confronts invaders with violence while Ms. Marvel's blue-skinned alien protector, Captain Mar-Vell, believes in finding peaceful resolutions. Their first appearance, as ordinary Army majors, contained another visual metaphor: Ms. Marvel wore a red scarf and Mar-Vell (disguised as an earthling) wore a blue suit.
The Heroes For Hire include hot-blooded Luke Cage and restrained Iron Fist. Their different temperaments get lampshaded while Iron Fist meditates.
Ozzy and Drix has this with a color inversion just like the movie it was based on, mentioned above, with Ozzy as the Red Oni and Drix as the Blue Oni. This is despite Ozzy being blue and Drix being red.
Other relationships show signs of this; for instance, Applejack is a Blue Oni to the more gung-ho and impulsive Rainbow Dash, but a Red Oni compared to the prim Rarity.
Ironically, despite being the Red Oni in pretty much any pair (except maybe when teamed with Pinkie Pie; that one has been shown going both ways), Rainbow Dash is a blue pony.
This is a list of the Mane Cast (and Spike) by order of most red to most blue: Pinkie Pie, Rainbow Dash, Applejack, Spike, Rarity, Twilight Sparkle, and Fluttershy
The Cutie Mark Crusaders count as well. Scootaloo being the Red Oni to Sweetie Belle's Blue Oni. Applebloom is generally the Blue Oni to Scootaloo, and can be either the Red Oni or Blue Oni to Sweetie Belle.
Also done with the Princesses, though played unexpectedly. Celestia, brightly colored Monarch of the Sun and the Day, is quite clearly the calm, rational, and wise blue oni while Luna, dark-colored Monarch of the Moon and the Night, is the short-tempered and emotionally driven red oni.
My Little Pony as a whole had several of these. The most obvious being Firefly-Medley and Cheerilee-Rarity.
Adventure Time: Marceline is a mischievous, loud, and careless Red Oni while Princess Bubblegum is a polite, calm, and caring Blue Oni.
The Simpsons: Impulsive Homer and practical joke artist Bart clearly form the Red Oni half of the Simpson household to pragmatic, tradition-worshipping Marge and bookworm Lisa's Blue Oni.
King of the Hill: Dale and Bill are generally the red, Hank and Boomhauer the Blue. Though Hank is dedicated to the point of near-blindness and refuses to admit he has an anger problem …
Ed Edd N Eddy: Eddy is short-tempered, has No Indoor Voice, hates following the rules, and follows his gut (Red Oni) while Edd (Double D) is willing to follow the rules, intelligent, rational, and thinks before he acts (Blue Oni).
Eds (relatively nice guys, trying to succeed via cunning rather than brute force) are blue to the Kankers' (blunt, insensitive molesters, always solving their problems by violence) red.
Samurai Jack has Jack and the Scotsman. Jack is quiet, stoic, and relaxed; the Scotsman is loud, boisterous, and passionate.
Tiny Toon Adventures has Buster who is the more intelligent and calm of the 2 stars as the Blue Oni, and Babs who is the more crazy and mischievous of the 2 stars as the Red Oni.
In the Disney Wartime CartoonReason and Emotion, Reason is the blue to Emotion's red. They even happen to be colored blue and red. The cartoon also argues that Adolf Hitler destroys the blue and plays on the red to gain power.
In Young Justice the main team has Super Boy, Kid Flash and Ms. Martian as the Red to Aqualad, Robin and Artemis's Blue respectively.
Jackie Chan Adventures has Jade being all impulsive, insistent, and violent while Jackie is relaxed, thoughtful, and peaceful.