Hi Charlie;

Tinted wood fillers that are latex/water based will allow the color to run and spread if you use (i.e.) denatured alcohol to wipe your surfaces before epoxying. Since it's not a bad idea to degrease before epoxying, that kind of lets those fillers out.

What I found to produce an almost invisible fill that sands, blends, and finishes without any surprises is yellow wood glue mixed to a _thick_ paste with wood flour that you mix for color. If you keep your sanding dust separated by color in a few cups you can mix up a pretty convincing filler. It does not change color after alcohol washing, drying, sanding, or glassing. Just be sure to use lots of wood flour and little glue.

Best Regards, Spidey