Red is picked up about half as well as green, and blue is discerned about half as well as red. You can definitely skimp on blue.

I strongly disagree. Blue is less bright to rods, that's it. If you happen to be looking at even gray, then sure the fact that blue seems a quarter as bright means you can chop off two bits. But if you look at pictures that are blue, without a lot of other colors to wash it out, you're going to have the exact same 450 distinct brightness levels over the 100:1 contrast ratio that the eye picks up.