CCD sensors used in digital cameras can't sense colour, only brightness. So how do you get a colour image? Typically by putting little red, green, and blue filters in front of the sensors on the CCD like the GRGB Bayer pattern depicted here. The camera software then has to do some funky tricks to compose a proper colour image.
Foveon has a sensor technology called X3 that works around this problem by stacking several translucent sensors in a single pixel. In theory this should give sharper pictures. So far the Sigma SD9 is the only camera out there with the Foveon sensor ($1500). Alas, the reviews suggest this first camera isn't quite up to the sensor.