[wcameron]

I don't think the aurora is a good example for reason you cited. The idea that we only see the aurora in shades of gray is false. I've sometimes been surprised by some extra color that the camera picks up but at least at upper latitudes the aurora's colors are bight enough to be easily distinguishable by the eye.

The tricky part with photographing auroras is getting the white balance right, as the unusual light source often confuses automatic color correction.