How to dye or tint epoxy resin to produce translucent colors?
You need something that's soluble in the liquid epoxy, or possibly a liquid that's miscible with it.  Water isn't miscible with epoxy, and if you try too hard to mix it you'll produce cloudiness. I suspect that rules out acrylic paints as well.  Typical solvents don't dissolve epoxy; some may be miscible.  I'm not sure what the liquid phase is to investigate solubility.

Powders in general - unless you want a glitter or speckle effect - are unlikely to work however fine you grind them.

There are specific dyes for epoxy (Amazon example), and this article also recommends alcohol inks - you can try making your own from old marker pens if you just want a test batch, though I'd use solvent-based markers to start with (such as Sharpies or cheap equivalents).  It would appear that alcohols mix with the solvents used in the epoxy components and in fact can apparently be used to thin epoxy.

You may have a little more trouble getting bubbles out than normal - a vacuum system is one way to help with this, but thinning should also help.