all of the atmosphere arts are sprites. basically images with transparent backgrounds, and they're all white. in runtime, they're tinted by picking the color at the center of the chosen planet. all of these white atmospheres are put into a Resources/ folder in unity so I can just do Resources.LoadAll that folder at the start of the game (which means i can just add atmospheres easily without ever manually wiring them in). I made them by applying various effects to glowing circles in Photoshop. The glow effect is, in fact, post processing. In Unity, if you go to your Render Settings, you can turn on Bloom. I just turned it on, adjusted it to a level that felt right, and that was all. I think I had to put the UI on a World Space/Camera Space Canvas instead of Screen Space to make sure it also got the bloom :)