They can be removed but require the rear quarter glass being removed by a auto glazer as there are rivets holding the trim in place behind it. A pain to remove in tact or without bending slightly.
As for colour coding make sure you take off the anodised coating before applying an aluminium etch primer or the paint wont stick for long.
You could of course have them anodised black once removed or black ones are available from Audi at roughly, from memory around the £150+ mark per side, for the Avant anyway
Hope this helps as i looked into it. Another option which i was about to have done was having them wrapped in vinyl by a sign writers