Maybe try this stuff?
I've never painted onto silicone, but this looks pretty good for it.

I have used silicone sealant (ordinary bathroom sealant) the stuff that you squirt out of guns. You can thin this down with either white spirit or lighter fluid and add silicone pigment or oil paints to acheive a silicone paint. You will need to experiment with the right amouint of each ingredient to suit your needs, and it sometimes cures quite shiny so you may also need to get a matting power to take the shine off the finished piece. Or if you are using platinum cure silicones such as platsil or dragon skin, you can mix part b with the desired colour, then add part a and thin with lighter fluid.