Sorry, also forgot to mention that your colours will shift with L or Ha RGB images (particularly with Ha). In most cases these will wash out the colour saturation which is easily resolved in PS. Depending on the object it is sometimes easier to replace the R channel with the a blended R and L or Ha image.
There is a good article written by Neil Fleming on the topic -
http://www.flemingastrophotography.com/lrgbshift.html