docs: we should explain colors (or at least think about how we are doing them)

[cafkafk]

Originally posted by @cafkafk in #1099 (comment)

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The screenshot doesn't make it clear what each color means.

I don't think we really document it anywhere either, but doing it by the color can be problematic because they're likely not gonna be the same for all users, so we'd have to document more just what color 0 means, what color 1 means, and so on.

If we do have that documentation somewhere apologies, I do think exa had it and a overarching philosophy behind the various colors. If we're still compliant we could also just copy that.