No, I don't think they lose color or discolor. I have a Red Silicon on a 12 I use on my Motorcycle and that's doing ok, even exposed to the elements as it is.Do the lighter colors discolor easily? Not just smudges, but actual discoloration on the sides like most clear cases… and the Caudabe synthesis I had for my 14PM I had dark green and the sides turned blackish after use. Very sad as I loved the case and strong magnet.
It is a soft-feel and "porous" maybe, so that's why I think it can stain easily.