You said, " warm/cool juxtapositions define form (which disappear in the b/w versions)?"
Yet, he is not defining "form" in the sky?
Also, if you are looking at the night sky and see something that you want to see better, then don't look directly at it and it will appear brighter. This is a common phenomenon. But unfortunately I can't explain it. I'll have to Ask Jeeves I guess.