There is a way to not end up with dark epoxy-based homemade filler. Thicken the epoxy with colloidal silica first. Since it's white, you'll end up with a milky colored paste. Then add your sanding dust (the finer the better) until you achieve the tint you're looking for. Start out with tiny amounts of dust as a little bit goes a loooong way toward changing the color.
Fillers are an el-cheapo way of doing stock repairs. I resort to them only when time/customer constraints dictate it. Solid wood "dutchman's" are a better, classier approach. Done properly with matching wood and exacting (patient) fitting they are harder to spot than any repair done with filler.
