There are several colors of transparent, fluorescent Lego bricks. In particular, "trans neon yellow" and "trans neon orange", introduced in the early 1990s, exist in a variety of specialized shapes like skis, satellite dishes and visors.
A Eurobricks discussion on why minifigs are not made from transparent colors suggests that the transparent colors require a different plastic resin than the normal bricks:
I think some of the issue is that (according to Jamie Berard [Lego designer]), the transparent bricks are made from polycarbonate plastic (PC) rather than ABS. And that's fine most of the time, when you've got opaque ABS and transparent PC, it works just fine. ... But when PC and PC parts get next to each other, they bond VERY TIGHTLY.
I've never really noticed this issue with transparent bricks, but perhaps it's only an issue for certain blocks or with the flexibility needed in minifigs. Still, it's good to know the characteristics of what you're working with!
I can find plenty of information about the normal ABS bricks, but little specifically about how the transparent neon Lego bricks are made. Are these bricks made from PC rather than ABS?