Mark Mandell - Gone Round In New Jersey
Lester,

I use TransTint [dye concentrate - in alcohol] to color epoxy all the time, sometimes in addition to wood flour or other additives, for filling. Using the dye (a drop or 2 is plenty) the epoxy will remain transparent, as opposed to using pigments or thickeners like wood flour.

Since you have open pore wood, you should seal the surrounding surfaces with something like shellac to prevent absorption of the tinted epoxy outside of the cracks. If your checks go through the board, you'll need to seal the opposite side and any exposed ends. While others may use masking tape for this, I find that it often leaks. Instead, I apply a wet coat of a wax emulsion like AnchorSeal and then immediately put a piece of Saran or other plastic wrap over the wet wax; makes a good seal if you support it by putting the workpiece on a flat surface. Attached is an example on Walnut. In this case, I wanted to accentuate the crotch crack that had bark inclusion, so I tinted with a medium brown