Paul,
When working on new recipes I always heat my plastic until it's clear and then add my colorant until I get the color I want. I've never had a problem with "clumping". What is happening to your plastic when you add colorant to it after it is hot?
From a technical perspective, colorant is just plasticizer with pigment in it. Plasticizer just softens the PVC. Other than it softening your baits, the only other thing it should do is cool it as it isn't 350 degrees when you add it. Is this what is causing the "clumping", is it just your plastic thickening because you are cooling it by adding a cool substance?
100 drops is a boat load of colorant for 4 oz. Fluorescents are really bad about hard packing on the bottom, do you have a few 1/2" nuts in them to make shaking / re-suspending easier?
As a side note, once I have my recipe down I cook my plastic with my colorant in it...
Sorry to jump in, just curious about the "clumping".
Jason