This is especially an issue for me, since I'm red/green color blind. I have trouble telling brown from forest green on a good day, and was shocked when I darkened a yellow and had people tell me it was brown.

The best solution is not to rely on color in the first place, since color blind people (like me) might not be able to read it. Not to mention there may be cultural associations you don't expect. For example, last year I would have combined blue and yellow only if I wanted extreme contrast, since each is the retinal after-image of the other. This year everyone sees them as the Ukranian colors.