basically you need to get to know your chameleon and learn what he shows you in a given circumstance. probably isnt a set meaning for any color a chameleon will throw. for instance, black can mean a few things but you will be able to differentiate once you get to know him or her. Black could mean "ahh, soakin up the heat" or "WTF is that, scared" or "I'm hurt" etc. Bright colors could also mean a few different thing but will depend on the situation to. for instance " Im content", "I hate you humans", "Im warm", "Hey Baby where you been all my life" etc.
in general though bright colors are good. although at certain times like basking dark colors are going to be par for the course.