[tab10672]

Kirk,
The plastic resin I used for the knobs i made is light cream color by itsself, you have to mix in the color dyes which is just colored part A. To create a swirl I mix the brown dye in to get the color I want then just before I pour it I add the black dye and barely mix it with a Popsicle stick then when I pour it, staying in one place as far from the mold as I can it swirls the black in with the brown as it flows through the mold. To make it more marbled I just mix in less of the last color and move around the mold as I pour it.
Your resin is probably different than mine but hobby lobby sells it if you want to swirl colors together it works really well and they have all colors of dye.