most of it depends on the depth of the rash, but just as any scar, the pink skin lacks as much pigment and doesnt have the same protection from the sun. so the cells arent mutated at all from the rash, but the lack of pigment left in your skin leaves skin at a bit more risk, just as scars from anything else would. but road rash is generally considered the same as a third degree burn, and can leave skin at significant risk to skin cancer at later times.. ive got some rash that ground down to the muscle. it looks fine now, just a little discolored, but when my arms get cold, the scarred part turns dark purple from the blood, because with the lack of pigment, skin is a bit transparent. i asked my doctor about it, and he said that i can never really go out in the sun again with out spf 60+, and even then not for long periods of time.
not trying to scare or anything, just giving my 2 cents. ask an oncologist (is that right? a cancer doctor...)
and at least for awhile if the rash was at all bad, use some spf 60+ when going out in direct sun.
spf 60 - you put it on, and the clouds come out, the sun dissappears, and its starts raining. obviously not really, but the stuff seems like paint when you first put it on.