There appears to be no way to customise colors used for text colors in the chat window. I have difficulty noticing and reading red text on a dark background.
TopHat, via wildstar-online

Although high contrast is beneficial for very large numbers of people and circumstances, very high contrast (black on white) can cause difficulty for people with certain forms of dyslexia.

Different colour combinations work better for different people, for example dark blue text on a light blue background can work well for some people with irlen-related dyslexia, and yellow text on a dark blue background can work well for cataracts, so the best possible option is a free choice of foreground and background colours.

But if a wide spectrum of options isn’t feasible, even a simple choice between high contrast and low contrast still makes a significant difference.

Best practice example: Runescape
Best practice example: Fallout 3