I was attempting to emulate the way it looks in real ife, since the moon appears brighter, the stars near it seem darker than the ones further away from it.

In this case sahding the turtles would only muddy things up. Its fine looking.

I think it's more than ok, I like these tiny ninja turtles! :P The only question is why did you make the stars around the moon darker. It's like they are in the corner of a room. Look at the stars, they don't change color (or brightness) when a I brighter lightsource appears. They are visible or not, it's this simple.