I often fill knot holes with epoxy dyed black or dark brown to look like sap or bark inclusions (either West Systems 105/205 or Starbond Black Medium CA glue work great). Lately, I have been using other colors to dye the epoxy for dramatic effect, such as cardinal red and blue. My results have been less than satisfactory. I have used Transtint (liquid and powder), and even milk paint. But the color is either very dark, or looks like weak ice tea. The color is especially dark with blind holes, which is most of what I am doing.
I'm looking for a true red, without needing light transmission from behind, as if you took red artist's oil paint and filled the crack. (I tried that too but the stuff never dries and does not take well to being sanded.) Also, many of the cracks are shallow, so a thin layer of translucent material ends up being less saturated. (Like when you look through plate glass and it is clear, but from the sides it looks green.)
Any suggestions? I have thought about the Smooth-on products, but they seem more like for stand-alone castings, rather than gap filling.
Thanks.