I used various combinations of liquid dyes and powdered makeup. If the powder wasn’t already loose, I scraped it off in thin layers with a knife. The color showed up in the opaque soap, but shimmer didn’t as much. Sometimes the powder stayed a bit clumped up, but I thought that was more realistically rock-life sometimes, so I went with it.
Below, I started out with pink, peach, and red shades using just liquid dyes in the white and clear soaps. These are actually from my first attempt, which I chopped up and reused, but you get the idea.