Rods pick up blue just fine, so I don't think you can skimp on any color.

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.