What would be a usable pigment brand to color the mixture of 100% silicone caulk and cornstarch in a body-safe way for making a pleasure toy? :)

I'm not sure about the safety of the 100% silicone caulk and cornstarch mixture but any pigment that is cosmetic-grade like those used for soap making would be safe on the skin but I can't guarantee the safety when inserted.

As far as the coloring goes though, usually when you use a pigment to color something, you want to glaze/gloss it over to seal the color. But I'm not sure how this would apply to your mixture. Hope that helps.