If you want a really good example, the northern lights are a good one. The majority of the color is something you cannot see with your eye because it's too dim for the cones to pick up. A camera doesn't have this limitation.
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.
The tricky part with photographing auroras is getting the white balance right, as the unusual light source often confuses automatic color correction.