Its something different, not found in stores. Every bait is unique. And I like creating baits that nobody else has, pure and simple. If I remember right you wanted a shiny bait and was painting or wanted to paint a stone mold to achieve this. The difference between a bait that has a slick finish or a matte one is that in the water the fish won't see a difference between the two from in the water.....they're both wet. That was the root of my comment. This surface pearling is color play, something that fish can actually see a difference or change in and is entirely different from what you were doing.
I have several stone molds for ring-bodied crappie paddletails that make baits with a matte finish as well as several cnc molds that make very productive, shiny surfaced baits. On any given day these dull baits typically out-fish baits with a shiny finish. Is it the finish? On that merit alone I don't think so, but I do know that when using any combination of the shiny or matte baits, changing colors can be a huge difference in catch or not catching fish and that the shiny or matte is a very moot issue. I pay close attention to color in my fishing, but that's just me. But its also why I try so many different schemes using a lot of the color shifting products. The color shifting pearls and surface brushing them to achieve what I get is fairly new to me [within the last year] so I can't honestly say that going to the trouble gets me any more fish. I do know from personal use that they do, in fact, catch fish.
If you feel that you'll gain something by painting the stone mold, have at it and let us know how it turns out. Something I would do before spraying an actual cavity though is to clean the stone on the outside of the mold well, make sure its totally dry and give the mold a shot of the paint you want to use and let it harden up for a couple days then try peeling the paint off using a sharp point of a small knife. If the paint holds, pour a little hot plastic on it and let the plastic cool, then lift it off to see if the paint holds tight. If it holds tight you're good to go. All of my stone molds have very fine ribbing on the bait's bodies. Painting the molds would more than likely diminish the space between the ribs and likely negatively affect injecting. If your molds are ribbed in a similar fashion I'd be very cautious of painting them.