I just made it back from backpacking (pictures forthcoming) in the Chisos mountains and figured I'd post a little short neato study I found since I'm way too tired to write anything with actual content (not that I ever really do anyway).
In the study, the researchers used genetic engineering to introduce a snippet of DNA that encodes instructions for how to make the red photopigment into the mice's genome. They then tested whether the mice could discriminate between two different colored lights.
Pretty neat eh!? Here's the msnbc write up.
-edit-
ahhh it seems The Loom actually has a very good post on this very topic! Go check it out!
I was in the Chisos doing biodiversity surveys last summer and absolutely fell in love with the place, hope you had a good time!
It was freaking great :)