Ah, yes, Paul - there is a similarity between the nebulae you describe and the aurora.
As explained in the link, with auroras, it's the photons emitted from excited oxygen (green in low + red in high altitudes, the latter less observable to human eyes)
and nitrogen (blue and pink).
And for both elements:
the more distraction from neighboring atoms (pollution, clouds), the less photons are emitted.
So intriguing - a whole new world of knowledge is opening a little gate via your posted image.
