The only way to get all the star colours is to have a high dynamic range. The sixteen bits of an astro CCD will give you 64k levels. The meagre twelve bits of a DSLR will give you about 4k levels. Both will saturate very quickly with the brighter stars if you are trying to collect dim nebular data with a reasonable signal to noise.
The pixels just outside the brighter stars have their colour information as a 'ring' of colour. This method may help if you don't want to go the HDR track. This would work better with larger image scales ie about one second of arc per pixel.
http://www.waidobservatory.com/tutor...tar-color.html
I have found that using HDR gives me 20+ bits of dynamic range ie 1M of levels before converting to LDR. This handles most star colours even with widefields where there is a very wide dynamic range. Just check out
http://members.optusnet.com.au/~avandonk1/rho.jpg
or any of my last few posts in deep sky at IIS.
Bert