One friend once told me that he would see 100% red down to 70% red as the same thing.

So after certain point, the intensity of red didn't matter.

Summer studies show that colorblind person don't get fooled by camuflage.

Anedoctaly, another friend got a LCD tv with a red dot in the middle of the screen. He sold the tv to the first friend because he had no problem with that dot...