I wanted to do this very simply so I painted a page of stars using black and grey. Here is the scan without any colour correction:
I did a levels adjustment to fix the colours, then cut out the stars. I tried the lasso, pen tool and eraser but in the end I actually found I liked the magic wand tool best as it preserved the uneven edges of the stars.
Here are the stars cut out and rearranged on a white background:
And here they are with a colour gradient:
Next I plan to play around with the colours some more and use these stars for a repeating pattern!