From what I understand most digital cameras have a sensor where each pixel-sensor has three sub-sensors, each one with an R,G and B filter. RGB is obviously the more fundamental colour model since it directly corresponds with the receptors in the human eye.
However, RGB filters necessarily cut out two thirds of white light to get their component. Surely cameras would benefit from shorter exposure times if the filters where instead CYM where each element cuts out only one third of the light? The camera's processor can still save the image in whatever format the consumer wants since a CYM datapoint can be converted easily to an RGB one.
I know this is sometimes done in astrophotography where three seperate B&W photos are taken with CYM filters.
Am I just wrong and this is, in fact, what's already done - or is there a good reason for an RGB sensor?