I've never tried anything else than pigments but maybe there was too much dye in the mix? Did the resin take longer to cure by any chance?
You could always the same silicone you used to create your mold to cast your rubber boots. Just don't forget to spray mold release or else you'll end up with a big block of silicone!
they might have taken a bit longer..just cuz they are thinner and i left them in the molds longer....weird thing is, i did pouches, grenades too and they are fine...course they are thicker....lol...