Start with a black layer (base, this one doesnt get touched), then add another black layer and add noise filter. Adjust levels to remove about 1/2, and to brighten the remaining ones.
Duplicate this layer, scale it up to make it bigger, repeat levels process til you only have a small amount. Only scale a small amount, they're stars not planets Link and merge the two layers.
Grab the eraser and just randomly remove about half the stars, just do streaks all over the place, make it messy.
Get the clone tool and set it to Screen, then clone bits of the stars into whatever shape you want, to get that star dusty type appearance. Fill in any black areas if you want, but make sure you leave some areas black so it looks random.
Duplicate the layer and add Gaussian Blur to it, enough to turn them into a big blob. Put the blob layer on top of the small stars layer, make it Linear Dodge. Adjust color balance on the blob to make a color. Duplicate the layer if you want it to be a bit more colorful, and also increase the blur on it about twice the size.
Now make a new layer, fill with black, set to Linear Dodge, and stick a blue lens flare on it, try to put it in the centre so you dont get the edges on it when you move it around. Scale it down to about twice the size of a star, then duplicate it and scale down half of that. You should have 2 flares, a big and small one. Stick these wherever you want, and duplicate them a couple more times to put more on.
Also, on mine I added an extra fat glow (by accident, but it looked cool so I kept it). Easily done by drawing a a fuzzy brush set to high size around in whatever shape, then Gaussian Blur it a lot, and adjust color balance. You dont need this layer if you want a realistic star picture.
As far as changing colors, so far the only way I've gotten it to work properly is by using Adjustments> Color Balance. Any other way just hasnt worked out. Otherwise you have to adjust layer properties so your whole layer doesnt get colored and its a mess, color balance just does it nice and quick.
Heres my .psd file with the stars on it, check the layer properties and stuff in case I forgot something, play around with colors, etc.
~3mb.
Also, for stars circling the planet, they were quick and easy. Just select the custom brush of the circle with transparent centre, make a long oval shape, fill it black, add noise, use levels to tone it down, use color balance to change color. Set it to screen so the black fill disappears and leaves just the stars. Rotate/scale/move, then erase the part that is supposed to go behind the planet.Dont need to do anything else.