I'd suggest a little blur on the tiny unimportant stars in the background (really little, like 1px); it helps keep them from looking like speckles or pixels.

Also, I'm assuming the colored ones are the important stars and the coloring is symbolic? Otherwise, I'd change that up a bit. Afaik, there aren't any green-spectrum stars, and even red/blue/yellow stars are really mostly white, so I'd brighten them and take down the saturation if you're going for true-color.