Hi,

Found on a European forum: if your plastic buttons lost some of the plastic tint:
well one can just use a very thin paintbrush and model black paint:

The previous button was quite damage, so we can see where there's pain on the above picture (still the guy tells he can't see it daily).
On these buttons... I can hardly tell where defects were (on the warning button according to the poster), so this worked quite well:


If your keys lost their color:



Ref 8Z0 837 891 A, 3€ (also available on Ebay)

 

Door plastic replacement/fix - one will need new door clips:


Using sand-paper and paint:
or get a new one:
New buttons:

Result:


Original forum in French: mon A4 et son évolution avec photos - Audi A4 - FORUM Audi - FORUM Auto par marques and mon A4 et son évolution avec photos - Audi A4 - FORUM Audi - FORUM Auto par marques