Today I would have just outlined all those black spaces, then scanned the page, filled the black spaces, and used the brush tool to pop out some stars.
Imagine doing this all by hand and outlining the stars rather than painting them back in.
This isn’t even my most ornate work!
If you were doing it by hand, wouldn’t you at least dot the stars in with white ink or white-out or somesuch, rather than colour around them? (OK yeah, you don’t always have good white ink on hand… or at least **I** don’t always. But still.) Granted, on Space Kid I do it by PC exactly as you describe here!
This was in my WHITEOUT-IS-EVIL days. And it usually is; it makes more problems than it cures.
GIMP eraser as whiteout, I LOVE YOU.