Stever, you've touched on a very sensitive bruise...Being a painters' board, the topic comes up on occasion. Plumbers (and even some carpenters) have all cursed us at one time (or every) by not only gooping up a fixture/wall gap with white or clear unpaintable silicone JUNK, but by oftentimes smearing the stuff far and wide on the walls, instead of on their faces where it belongs...
I remember darn near 20 years ago I was on a crew repairng holes in a domed sports arena at the University of Wyoming in Laramie, using (I believe) either GE Silproof or Dow 790 or 795...It's been too long...But anyway we had to make the silicone patches paintable, so we used a specialized primer specifically made for silicone...The stuff cost over $100/quart, however, and could NOT make contact with the skin...It was clear and had the consistancy of cyanoacrylate (superglue)...
I sometimes get lucky and with enough coats a silicone bead will cover--Not bond, mind you, but cover. Our best course is to educate plumbers to change their choice of material...The problem is that I've usually ruined every opportunity by telling them how stupid it is for them to use unpaintable sealants...You can tell that I'm not a big fan of plumbers...
Another course of action, one that I've resorted to more often than not, is to simply cut out the silicone and lay a new bead of paintable sealant. My work
always looks better than theirs in the first place, and it does't take me too awful far out of my way, in most cases...