Joined: Jan. 2006
Regarding color and toxicity...
If many edible mushrooms have various flashy colors (which can be the case), having such a color would not be a clear advantage for a poisonous species.
And we still don't know whether most fungivores are able to distinguish between colors (I bet slugs are not good at it).
We know that pigments are relatively costly to synthesize for an organism. There must be some selective advantage, evolutionary hitch-hiking would not be sufficient to explain their maintenance.