We see that for the first stage, Falcon 9 boosters, SpaceX barely cleans the soot off. (Generally the soot comes from flying through the engine exhaust of boostback, reentry, and landing burns.)
The Dragons come in looking mighty toasted as well on the upper shell.
On the booster, ready for launch they look much cleaner.
Does SpaceX clean the upper outer shell or replace it between launches of a Dragon (Crew or Cargo, does it matter?)?