We need some studies on the taphonomy of color.
My impression is that color is preserved in certain circumstances,
including species-specific aspects. Organic rich and/or
anoxic deposits seem to preserve color sometimes, whereas others (oxic?)
do not. Certain gastropods seem to show more color whereas
others have no color when alive. So a taphonomic review would run
the entire gamut from living through fossilization to collection by
paleontologists (do we pick out the colored ones more than
others?).
Probably a couple of Ph.D dissertations in this, at least. Maybe
some have been done, but more could be done I'd bet.
Jere