As I commented elsewhere - this is a expertly processed image and it's hard to believe this is from, essentially, a DSLR that anyone can buy (if, for a moment, we forget the mods and hard work that went into upgrading it
). These are exciting times for astrophotography!
The color constancy algorithm does wonders here for negating the effect that stretching the image has on the coloring in the image (which alas is still a common issue in many images - colors in deep space don't magically change out there just because you picked a certain exposure time!). It's wonderful to see, for example, M4 carry stars with different colour temperatures, regardless of how close those stars are to the core; if colour was captured by the CCD for something, it is retained and the relative brightness of it is ignored for deciding what color something is (as it is arbitrary).