You'd have 4 pixels per pixel so to speak. This is the concept like the Foveon (but that uses silicon depth/wavelength response so the sensors are "stacked" instead of a group of 3 (lum is missing , at least as a seperate pixel) or the Nikon patent:
Nikon's new full-color RGB sensor?: Digital Photography Review 
The pros and cons of Bayer types vs these types can be researched.
The only real problem would be well size and the need for a pretty heavy processing pipeline.
EDIT: And we can all join the is it 14mp or just 3.5mp (3.5mp would have 14m(p) sensels) debates that plague the Sigma owners..