Why is the color Red and Blue considered opposite in human culture?

by Weiss-Ruthenien

Here are the following list of such phenomenon:

  1. Roman Optimates faction used blue as color, while Roman Populares used red.
  2. Minamoto clan during Genpei war used blue-white colors from Rigel to represent them, opposed by Taira clan that used orange-red colors of Betelgeuse.
  3. The Byzantine Empire traditionally used purple and blue, while a new rising powerhouse, the Ottomans adopted red.
  4. Most famously perhaps, the identifying color for NATO is blue, and those of Warsaw Pact was red.

I do get blue usually represent Nobility and Red represent Commoners, but are there any research on this?

OstapBenderBey

In simple terms, red and blue were the most highly available and colourfast colour dyes so the obvious colours to use for military flags and uniforms.

In ancient Roman times the main dyes were woad (blue), madder (red) and weld (yellow). Weld wasn't very colourfast (it would dissipate over time) so wasn't common in uniforms or flags.

The Romans also had other colours like Tyrian Purple (from crushed snails), crimson (from crushed insects) and a more colourfast yellow (from Saffron) however these were much more expensive and therefore typically used by nobility only.

Lighter colours were very possible from dying briefly (light blue and red/pink) however needed care to apply consistently so less suitable for an army. Overdyes where the colours were combined (to green, orange, purple) were also possible however again not likely for an army as the process was more complex, the yellow component would still fade if in use, and the purple wasn't nearly as vibrant as the royal (Tyrian) purple. Lichens were also used sometimes for greens and purples however again not as widely available or colour fast.

In Japan there were different plants but a similar mix of colours. 'Benibana' (safflower) for red, 'tadei' (a form of indigo, which has the same basic chemical as European woad) for blue, and 'kariyasu' (a grass) for yellow. I believe the Japanese yellow is, however, more colourfast than European weld.

I don't know the exact plants in the Byzantine / Ottoman empire but the story would be similar.

With the age of empires came a broadening of the palette however broadly the cheap, natural dyes all had similar colour ranges. It wasn't until the 20th century that synthetic dyes really enabled the cheap production of a broader range of colours.

I'll mention the NATO and Warsaw Pact colours just briefly for their own more modern history. The red of the Warsaw Pact comes from the socialist 'red flag' which was used at least as far back as the French Revolution of the late 18th Century. At the time this was used against the French monarchy (traditionally blue in colour) however conflicted with the Church (also red). Over time it has developed a symbolism of the 'blood of the workers'.

The NATO flag is therefore the only one that really comes from a modern era where any colour could have been reasonably used. The official answer is that the blue represents the colour of the Atlantic Ocean.

OmegaGreed

Not to dissuade you from seeking answers here, but this might be a good question for /r/AskAnthropology or even /r/askscience as well.