Are your epoxy dyes and pigments transparent or opaque?

Either. Any Pigmently color can be transparent or opaque depending on how much you add. A small amount gives a see-through tint; the more you add, the more solid the color becomes. The pigment-to-epoxy ratio is unique to every project, so if a test batch comes out darker than you wanted, simply use less next time.

The two types behave differently:

Liquid dyes are flat, straight colors with no pearlescent effect, and they are naturally more translucent. Roughly one bottle per mixed gallon gives a translucent color; a fully solid color can take 2 to 3 bottles per gallon.

Mica powder pigments give a richer, pearlescent tone, add depth and swirls, and go much farther than liquid dyes, so they are the easier way to get a solid, opaque color. For a solid color in 3 Gallons Combined of UltraClear Bar & Table Top Epoxy, one or two 51g containers is enough.

So for a transparent, stained-glass tint, use a little liquid dye (or a little powder). For solid coverage, choose a powder pigment or add more liquid dye. Colors in photos never match the true color exactly, so order the 5g powder or 10ml liquid size and test on a small scale before the full pour.