So if you have a dark background, you wanna copy the color of it. Paste it as the color of your glow. Take that color cursor and move it up a bit, so it's brighter... then check that box that says "blending" so it instantly looks better
This is a rough layout of what my level looks like so far :D do you think you could put it into an actual level in GD? If yes can you extend it and improve it (as well as turning it into an easy demon)