On 28 Feb, 09:49, Stuart Noble
wrote:

Cement powder dyes would probably be ok and are easy to find.

Not a vast range of colours though. Purple isn't cheap!

Cement stains are pigments, rather than dyes, so there can be problems
in getting a good mix if you put them directly into epoxy. Easiest way
is to wet them with a spot of acetone first, then mix that wet into
the epoxy.