ICE Resin is very easy to color. You won't need any special colorants as you can add anything that is oil based or dry. Only make additions after you mix the resin thoroughly so you get a good cure result.
Oil Paint is handy and easy to blend to get special colors. A very tiny bit creates a lot of color, a bare touch of a toothpick is good for sheer color.
For a really deep color, add a bigger chunk and a tiny extra squirt of Part B Hardener to the resin to compensate for the change in formula. (You don’t want to do this with a clear resin pour as it can cause a yellow cast)
Another way to color resin is to add mica powder for a lovely swirl of intense color.
Glitter can color resin if used en mass. I love to put “Cup Chain” in when using clear resin as it reflects the light just like the chunks of Glass Glitter. Flat backed crystals just disappear when put them into clear resin.