Often the cheapest way to go is use the same silicon your part is made from and mix with oil based paints. The off-the-shelf painted I have used are nothing but that, but with a huge price tag. For example, I painted the Creature from the Black lagoon masks for the really bad stage musical they did at Universal Hollywood. The masks were made with Dragon Skin, and to paint, I mixed oil based paints into a small batches of Dragon Skin, and thinned with Toluene. WEAR A RESPIRATOR!
Charles