Trying to prevent blending of color layers

This question comes through email by Angel:

I am going to try using opaque resin in a silicone mold. I usually work with polymer clay and plaster. My question is, if I want the main part of the mold to be opaque, can I put colored resin on top of that without it bleeding down or must I wait for the opaque layer to cure then fill the rest of the mold with a colored resin. Thank you.