What's the exact opacity and translucency of transparent bricks?
I have a couple friends in the LEGO company, so I asked one of the guys behind piece creation about this. It turns out that TLC itself doesn't have this information.

The problem is,  lab-testing the exact opacity and light absorption depends on certain ideal conditions. These conditions, like for any test, require the material to be identical in every way to the other materials except for the tested variable.

But there is no piece that comes in every color! And even worse, each batch varies slightly from the others. TLC's QA department is good, but not that good. 

So while this is certainly a worthy concept to test, you will likely find that your own results will be the most thorough ones you can get. I recommend that you personally do whatever you need to find your answer, and maybe tell us in a comment or on chat what you found!