EXCELLENT NEWS! I’ve solved the mystery of the semi-transparent icons.
Motion blur. Yes, motion blur. I had pre-comped the Particular layer with its camera, and the motion blur switch was checked for the Particular layer. When I turned off motion blur on that layer, and that layer only, everything was 100% opaque, just as it was supposed to be.
When I discovered this laughably simple solution, I was worried that I wouldn’t be able to have any motion blur on my particles at all. I didn’t mind that for the pre-comp because it was supposed to be a relatively static field with the camera moving through it. Little to no visible motion blur anyway. However, the whole particle system is subjected to some pretty gnarly motion in the context of the whole project. Luckily, that motion blur remains unaffected, and I still retain my desired results. Hooray!
I still have to do a final render at full res before I know for 100% sure that everything is OK, but I’m confident that my test results are indicative of a case closed. If you don’t hear from me tomorrow, it’s safe to assume everything worked out.
Thanks everyone!
Zak