Model company Tamiya has a logo consisting of two white stars; one on a red background, one on a blue background. And indeed, the red star stands for passion and the blue one for precision.
During the Cold War, communist countries were represented by a red star, symbolizing the passion associated with revolution and subversion of "the system", while capitalist ones were associated with the color blue, representing the "cold" and calculating nature of the capitalist ethos.
Inverted in American revolution, where the British already had red uniforms and the revolutionaries were left with blue (when they had uniforms, anyway).
Now in the USA, Red represents Republican states or regions, Blue represents Democratic states or regions.
Played straight as far social issues go. The red Republicans are as a whole more passionately religious, containing the Christian right, and supportive of laws pushing a certain moral view point, and also support gun rights and are more likely to be War Hawks. Democrats on the other hand support a live and let live mentality concerning social rights, except when it comes to supporting gun control, and are more likely to be Peace Doves.
The colors were arbitrarily changed around until the 2000 presidential election, where Tim Russert started talking about "red states" and "blue states" and the monikers stuck. The old way can be seen in older institutions like National Review. The website's masthead and the borders of every issue's cover are blue and always have been.
And reversed in the United Kingdom and Canada, where the main left-leaning parties (Labour and Liberals, respectively) are identified by the colours red and yellow, while their opponents in the Conservative Party are identified by blue. In this case, the use of red is derived from the socialist and social democratic associations of each party, while blue was traditionally associated with the monarchy and other such traditional institutions.
Red-left and blue-right is the standard in most of the Western world for the reasons listed in the UK and Canada entry above. American conservatives can be heard, from time to time, lamenting being assigned the "wrong" colour in a freak occurrence. For example, the Cold Warrior line "Better dead than Red" no longer holds in domestic politics.
Coca-Cola and Pepsi. Coca-Cola has survived by its aggressive and continual marketing campaign and bright, memorable advertisements, is incredibly popular, and is sold in red cans. Pepsi has a much more subtle presence in marketing and is sold in blue cans. On the other hand, Pepsi is totally the Red Oni, in spite of the can color. When their ads do show up, they're all about aggressively taking potshots at Coca-Cola. Coca-Cola's marketing generally involves adorable polar bears quietly enjoying a refreshing Coke.
This is even true for the way both taste: Pepsi has been described as being extremely sweet, almost aggressively so, while Coca-Cola is a lot more mellow. The differences in taste has led to them preforming differently on various kinds of taste tests.
Theodore Roosevelt and Woodrow Wilson, the two famous Progressive-era Presidents. They aren't color-coded, but they fit the personalities well and the colors associated with their modern day parties.
Theodore Roosevelt is also the Red Oni towards his Secretary of War and Presidential successor William Howard Taft, who was definitely the Blue Oni. The boisterous TR was also the Manly Man to Taft's Sensitive Guy (that's right, folks, TR was such a Manly Man that he was more of a Red Oni than his own Secretary of War!). TR endorsed Taft to succeed him in the 1908 election, but soon grew impatient and dissatisfied with the Taft administration and ended up running against him, first in the GOP primaries, and then running with a brand new party of his own creation when he lost the primaries.
Admirals Halsey and Spruance who regularly exchanged commands of the Central Pacific sub-theater in World War II. Halsey was the Red Oni and Spruance the Blue Oni. True to form, Spruance was in command at the Philippine Sea, and in true blue nature stayed near the landing fleet to protect it, and was harshly criticized for not pursuing the Japanese carriers. Next, Halsey was in command at Leyte Gulf, acted in predictable red fashion by pursuing the Japanese carrier fleet, and was harshly criticized for not protecting the landing fleet. The Japanese even planned for this (although they didn't realize the two commanders were swapping out the same fleet), taking advantage of Spruance by hanging back farther away than he would venture and launching attack with their longer-ranged planes, and taking advantage of Halsey by luring him away with a token group of carriers that had almost no planes on board. They still ended up losing both battles decisively.
Robert E Lee's two wing/corps commanders in the Army of Northern Virginia (Lee himself was more of a Purple Oni and fit both stereotypes) - Red Oni Thomas "Stonewall" Jackson and Blue Oni James Longstreet.
McCain was also a Red Oni to Mitt Romney's Blue Oni, and Obama played Blue Oni to Hillary Clinton's Purple Oni (some Red Oni traits, some Blue Oni traits) during the respective primaries. Mike Huckabee was arguably another Red Oni, although he doesn't fit it quite as well as McCain (Huckabee is often just as fiery when talking about issues, but otherwise seems quite personable, even to opponents, so he doesn't quite fit the Red Oni designation as well as McCain). So perhaps he'd be a Green Oni?
Speaking of Mitt Romney, as of the 2012 Republican primaries, he's now the Blue Oni to ALL the other candidates' Red Onis! And not surprisingly, within the Republican Party, those who favor the Blue Oni approach to campaigning—i.e. focus on the economy and don't bother with the fiery and divisive "culture wars" issues—seem to be lining up behind Romney, while those Republicans who favor the Red Oni approach, where the "culture war" issues are front-and-center, are divided between Newt Gingrich (who's the most Red Oni personality-wise too, in stark contrast to Romney's Blue Oni temperament) and Rick Santorum. Oddly enough, there's also a second category of Red Oni in this year's GOP primaries: Representative Ron Paul and his supporters, who, interestingly enough, support a platform that avoids the "culture wars" issues, which should put them in the Blue Oni category, if not for the fact that they are so loudly passionate about it that Ron Paul and his supporters' approach is definitely Red Oni, despite the fact that their actual platform seems more suited to Blue Onis.
Sarah Palin is also a Red Oni to Obama's Blue Oni; McCain would also play Blue Oni to Palin, but only really in comparison. Similarly, Joe Biden is the Red Oni to Obama's Blue.
Bush was also a Red Oni to Dick Cheney's Blue Oni.
In the 2004 election the Bush (red)/Kerry (blue) contrast was striking (almost as much as Bush/Gore in 2000). Edwards would have been the red VP to Kerry's blue had they been elected. (As for Gore and Lieberman, it's hard to say which one would have been the red because they were both fairly blue.)
Other Presidential election contests: 1960 had red Kennedy vs. blue Nixon; 1964 had blue Johnson vs. red Goldwater; 1968 had blue Nixon vs. blue(r) Humphrey vs. red Wallace; 1972 was blue Nixon vs. red Mc Govern; 1976 was red Carter vs. blue Ford; 1980 was blue Carter vs. red Reagan; 1984 was red Reagan vs. blue Mondale; 1988 was red G.H.W. Bush vs. blue Dukakis; 1992 was red Clinton vs. redder Perot vs. blue G.H.W. Bush; 1996 was red Clinton vs. blue Dole.
Recent President-Vice President pairings: Reagan (red)/G.H.W. Bush (blue); G.H.W. Bush (still blue)/Quayle (red); Clinton (red)/Gore (blue); G.W. Bush (red)/Cheney (blue); Obama (blue)/Biden (red). Ryan would have been red to Romney's blue, and (as mentioned above) Palin would have been red to Mc Cain's blue (although both were fairly red overall).
Other President/VP pairings: Kennedy (red)/Johnson (blue); Johnson subsequently turns red to Humphrey's blue; Nixon (blue)/Agnew (red); hard to say with Carter and Mondale (both fairly blue, Carter probably the red of the two though).
The 2012 Presidential election has rivals Rick Perry, a Red Oni, and Mitt Romney, a Blue Oni, Michele Bachmann, another Red Oni, and Newt Gingrich, another Red Oni. Herman Cain and Rick Santorum have both Red Oni and Blue Oni qualities, and Ron Paul would be a Yellow Oni.
A slight inversion with ex-presidents turned best buds, George W. Bush and Bill Clinton. Democrat Bill is the Red Oni, while Republican Dubya is the Blue Oni.
South Korea's flag is the yin-yang with blue and red instead of the usual white and black.
South Korea itself is the restrained, well-behaved sibling of the boisterous, blustering North.
Unsurprisingly, siblings can be like this. This is especially pronounced when they're twins, or when there are only two children in a family. For larger families, there may be more than one red/blue sets.
Lampshaded in the Rally to Restore Sanity and/or Fear, in which Stewart rallied for "sanity" while Colbert rallied for "fear".
L.A. street gangs, the Crips and the Bloods, wore blue and red bandannas, respectively, to distinguish themselves. Whether either group tended to be more emotional and hot-tempered, though, is up for debate.
Swedish monarch Gustavus Adolphus and his chancellor Axel Oxienstierna, at least in Hollywood History. An anecdote has an exasperated Gustavus telling Oxienstierna "If it wasn't for me, this country would be frozen solid!" and Oxienstierna calmly replying "And if it wasn't for me, it would be burnt to ashes."
Queen Elizabeth II is the blue oni - blue is her favorite color and all - since she is so prim and proper, always practical and no-nonsense. Her late sister Margaret was the red oni. Which one is the Tomboy and which one the Girly Girl is harder to determine.
Elizabeth was the tomboy because she is technically an army officer.
Another example of siblings fitting this: the Gyllenhaals. Look at their film roles and their offscreen personalities: Maggie is the Red Oni and Jake is the Blue Oni.
There are two main different types of personality that define this trope - Red Oni is extrovert and Blue Oni is introvert.
Richard Feynman and Julian Schwinger. Feynman was rough, energetic, informal, and uncouth. Schwinger was dignified, reserved, formal, and proper. They took completely different approaches to quantum electrodynamics and came up with essentially the same solutions. They (along with Sin-Itiro Tomonaga) shared a Nobel Prize for this work in 1965.
In Australian Politics, Opposition Leader Tony Abbott plays the Red Oni to the Blue Oni of Prime Minister Julia Gillard (and her immediate predecessor Kevin Rudd).
In a similar case, Patton and Montgomery. Patton who is an aggressive newbie, and eager to get to the front while Monty is a reserved veteran and has more experience in fighting the Germans. In a subversion, however, Montgomery was one of the few equal matches for Patton in terms of ego and boastfulness.
In yet another case, Patton vs Rommel. Again, Patton was the red oni while Rommel was the blue one. The Hot-Blooded Patton even named Rommel a calm Magnificent Bastard.
However, John also served as the Blue Oni to his cousin Sam's Red.
Jefferson was himself the Red Oni to Alexander Hamilton's Blue Oni when the two men served as secretaries of state and treasury, respectively, under President Washington. Jefferson was also Red Oni to James Madison's Blue Oni when Jefferson himself became president and Madison his secretary of state.
In the US Congress, the House of Representatives is often considered the Red Oni to the Senate's Blue.
Among the First Triumvirate in Ancient Rome, the red was Pompey the Great, the fashionable and charismatic maverick who loved the spotlight, and the blue was Marcus Crassus, the behind the scenes wheeler-dealer who preferred to stay in the shadows. Gaius Julius Caesar fell somewhere between the two.
Prime Ministers William Gladstone (red) and Benjamin Disraeli (blue).
Cats and dogs can be stereotyped as this, with dogs (Red) being more outgoing and energetic and cats (Blue) being more independent and reserved.
Former French President Nicolas Sarkozy (red oni), and his Prime Minister François Fillon (blue oni).
In the Chinese Civil war the Communist Party of China who are the red communist, to the blue nationalist Kuomintang. Today they are the People's Republic of China, and the Republic of China respectively.
Chairman of the Communist Party of China Mao Zedong was the Red to Premier Zhou Enlai's Blue.
In pathology, bacteria thrive in hot, marshy, and tropical environments (red oni) while viruses thrive in cold, boreal, and tundric environments (blue oni). Both can infect mammalian life of any kind and can prove difficult to eradicate.
The two most common Doritos flavors are Nacho Cheese and Cool Ranch. They fit the red oni and blue oni labels in both packaging and taste.
The four temperaments have this trope down too. Cholerics and Sanguines are described to be Red Onis while Melancholics and Phlegmatics play the Blue.
The Apostles St. Peter and St. Paul. Peter was the Red Oni (think him about striking the ear off one of the Roman soldiers!), while Paul was the Blue Oni (he had studied under Gamaliel the Great and was very eloquent).
Steve Jobs (red) and Bill Gates (blue).
Jobs and Wozniak also fit.
The co-emperors of the Roman Empire after the death of Antoninus Pius fit this. Lucius Varrus was the red, with Marcus Aurelius being the blue.
Mark Antony and Octavian from the Second Triumvirate.
In his book Thinking Fast and Slow, the behavioral psychologist Daniel Kahneman posits that people use two different modes of thinking: one that is "fast, instinctive, and emotional", and one that is "slower, more deliberative, and more logical". Extend this to distinguish the types of people who rely more on the first mode and those who rely more on the second, and you have some scientific basis for the existence of this trope.
Adolf Hitler and Josef Stalin. In public, Hitler was the Red Oni. During his speeches he was very animated and explosive, whipping himself and the audience up into a frenzy. Meanwhile, Stalin's speeches were more dreary and tranquil, making him the Blue Oni. However, in private, it was reversed. Those close to him described Hitler as being very relaxed, simple, and easygoing. Some historians have even pointed to Hitler's easygoing nature as a reason for losing the war. He often shrugged off problems that later became much bigger problems, such as Hermann Goering's repeated failures with the Luftwaffe. Stalin, on the other hand, was known for his sudden fits of rage and paranoia which usually led to the infamous Soviet purges. More high-ranking Communists were actually killed by Stalin than by Hitler.
The three major countries on the North American continent: Canada (Blue), Mexico (Purple), and the USA (Red).
In the past during the Cold War, of the two major communist powers the USSR was the red (active player in the Cold War and the worldwide spread of communist ideology) while China was the blue (more inwardly-focused on building China and, as they have been for much of history, aloof to global politics). Now, arguably, the roles are reversing: Russia (no longer communist) is stagnating demographically and playing mostly rearguard militarily (blue) while China ("communist" in name only) is becoming more dynamic and assertive economically and militarily (red).
Athens (which valued learning and culture) was blue to Sparta's red (where military glory was valued).