I tend to use one layer of fairly short exposures like 12x30sec for each of RGB and this is my 'star color' layer. When all of R/G/B are very close to 1.0 (full CCD range) there is no color data any more. To get star colors one must avoid over-saturating any of the R/G/B layers. Even if one layer is saturated to max CCD ADC or even over 80-90 percent you distort the color data.
You can then separate this color layer out after much boost to it's saturation to peel off the color data without the luma (separate out to Yuv sort of layers). This color data can be combined back into your star luma data for more colorful stars.
Be careful in your stretching of r/g/b and use a curve that brings up lower levels but does not as greatly amplify over 40% signal. This curve must always be increasing slope (gain) but just not as much gain to the over 40 percent already hot stars.
There are likely many tutorials but I had to mess with this problem for many years especially if you want those stars to have nebula all about them. Every images is a bit different so there is no one stock formula except in general terms mentioned above.
good luck,
Mark
www.astrospotter.zenfolio.com is where my images live