whenever you're done with your project, make new layers that you set as either "color" or "overlay" depending on how it comes out and use the gradient tool. Choose the color you want and apply the color gradient on those layers. You'll see the piece will change color in a cool way. Sometimes it's not strong enough so duplicate the layer. Feel free to use the transform tool (control T) and change the size and all of the gradient. Then play around and use as many gradients and layers as you need. The more you practice this, the more you'll get used to it.
Lol I'm sure real-life space isn't as colorful, it's probably different. Still it's really cool to check out pics from NASA I feel so geeky when I do it though. Hehe yeah I really wanted to blend colors that are unusually blended. Like red and green, they're complimentary colors so they have a hard time blending. So it was a challenge for me ^.^