Wow, there is just no easy answer to that question. Could it be a breeding issue? yes if they never had good color, and no if they once did.
I've had RCS for almost ten years now and the colors are just as good as back when. Stress in Neocaridina sp. cause them to lighten. It could be water quality, over feeding, having fish in the tank, sickness, just to name a few.
You also said many...is that like half? Males are lighter in color than females.