Hi Harry,
to increase saturing star colours I use Curves Transform, Color Saturation is too much agressive for my pleasure, I use an specific star mask not inverted constructed without scales beyond of 32px as they say the tutorials, when I have star mask applied on the image open Curves Transform and I operate on channel S and channel C, when I finish with this open Morphologycal Transform and I reduce the size of stars by means of the circular structure> Minimum Filter.