I'd try a darker shade of red/burgundy as alternative to blue. And I'd use a different color for the cluster names. Also, I'd probably do the tertiary as a triangle, not a line, or try to overlap them more, though that's probably only really nice when the stars have different colors.
Thanks for the feedback. Overlapping stars more looks really bad, even if they are of different colors; it just makes things too messy. I think I didn't try a triangle arrangement, I guess that could work. I'll have to try it. Yeah "sector" or "region" names probably need a different color. I tried a few, liked none.