system
Given the following post, respond as if you're commenting on Reddit:
human
[Avatar] Why do people of the various nations continue to color code themselves?

In TLA I can understand the various elemental cultures wearing similar colors: it's a less connected world and harder to ship goods around, so I assume they use locally sourced dyes for their clothing (Easier to fine green/tan dyes in earth bender regions etc.) Why though, by the LoK time period do the four major tribes people still stick to Blue/Green/Red/Yellow for their clothing? There's huge national navies so one can assume civilian trade has spanned the globe much more thoroughly, and Republic City is intentionally a mixing pot of culture.
gpt
Three reasons:

- As you mentioned, in Aang's time they were probably using locally-sourced dyes. While things are more connected in Korra's time, local is still usually going to be cheaper (especially if you're not in somewhere like Republic City). They're not quite to the point where it's cheaper to manufacture everything in the Earth Kingdom and ship it around the world.
- It's the traditional style of their homelands. Not everyone is super patriotic, but most people would at least have some kind of fondness and connection to the culture of the place they (or their ancestors) came from. Sure, Varrick *could* get some fine red clothes from the Fire Nation (they make the best red stuff there), but he *likes* Water Tribe blue.
- People in Avatar-world tend to have eye colors that match their ancestry and/or bending type. Mako has reddish eyes, Bolin has green eyes, Korra has blue eyes, and Tenzin has gray eyes. This isn't absolute - Asami actually has greenish eyes despite having Fire Nation ancestory - but it's common enough to reinforce the trends. Fashion-conscious people would gravitate towards color palettes that complement their eye colors.

These things'll probably fade over time, but for now it's only been 70 years since the end of the Hundred Years War. The world hasn't been connected that long.