Don't try taking these apart and painting them - I tried it without success - but perhaps I didn't try hard enough...
What I did notice by chance however, was that when I scratched one of them with something sharp - the original color came through a bit!
They are made of some hard sort of rubber (I hate to say plastic, because plastic seems usually to be a lot harder and brittle than the "rubber" the switches are made of.
Through the passing of years, this "rubber" the switches are made of appears to get discolered by the sun and the elements and loses its original grandeur.
I tried scratching very gently on the surface with a flat screw-driver, and to my amazement it started coming nice again!
(Note, VERY gentle scrapes - you don't want to destroy your switches!).
Also, I tried fine grained sand-paper (water paper actually) but this just seemed to make more a mess of things.
So, with patience and gentle "scrapes", I did this all over each switch: