I mixed to quarter-sized batched of epoxy: to one batch I added one small drop of acrylic paint and to the other I didn't add anything. I didn't glue anything to the batches, just cure on a plastic surface.
A drop is too much in my experience. I mix my epoxy on some wax paper. I put a drop of color next to it, and when I'm mixing it, I take a toothpick and get just a bit of the color (much less than a drop). All you want to do is tint the epoxy. I have noticed that using to much will affect the glue setting up. I've never had a failure, but like you said, it's rubbery.
Frankly, if you paint the inside of the blank thoroughly, I don't see a need to tint the epoxy. I pretty much have quit doing this step. But I've done it a lot i the past with great results.
Tony i had a pink one like that and painted silver and didnt like how it turned out. was kind of muddy looking. So i think your idea of painting the color of the blank would work better for these super transparent blanks.
I use a medium silver/gray. A bright silver is similar to white. In most cases it will dull the blank. And I only use silver if I have multiple colors that are translucent. If you have just 1 color that's translucent, do your best to match the color. And in most cases I go a shade darker. If in doubt, then use the medium silver.
What I was told a long time ago was to think of the paint as primer in car painting, only in reverse. If the blank is really clear, then it's basically a tinted clear coat. You can't put primer (silver) directly under that. Do a coat of a matching solid, then after that dries to the touch, put the silver/gray next. Depending on the hole size, you may need to drill a slightly larger hole, or sand the hole. If it's a really clear blank, sanding may be required anyway to get the drill marks out of the blank.
Some people don't want to spend the time doing this much prep work. But the results can be stunning.