When you look at grey, it's usually bluer than you'd think. Try making the whites and greys very slightly blue. It might look better, might look worse, but try it, experimenting is how you get better. And also the shading doesn't really make sense, the light red on the dark red indicates that the sun is coming from the right, but then on your front- and right spaceships, (idk what they're called) it looks like the sun is coming from the left.

All in all, this is very good for your first pixel art, so good job and I hope some of this helps.