Can a dye or food coloring be mixed in to get a bright color that contrasts with the wood? Like the dots on LBD's Dice Puzzle. I.e. bright red, yellow, green etc. Maybe to show a colored line that contrasts.
I'd suggest something like Mixol. It's a pure pigment and won't affect the epoxy significantly.
Also, I've been using System Three epoxy paste quite a bit lately. It's easy to work with and I get good results with it.
If you use any other products besides the Mohawk shown above, the 20 to 30 minute period might be off for when it's gotten to a state where you can carve and plane it. What I like to do is keep a little of the epoxy I mixed for the fill on the side and monitor its progress every so often until I think it's ready.
Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner