The mosaic of microscopic color filters laid over the sensor. The light-sensitive diodes are themselves colorblind, so each is given a red, green, or blue filter: one row alternates blue and green, the next green and red, giving the array twice as many green pixels as red or blue. The camera reconstructs full color from the mosaic by demosaicing.
The reconstruction of full color from the Bayer mosaic. Each pixel behind its single filter is a pixel well that knows one color's brightness and nothing else. The processor walks the entire sensor and, for every pixel, reads it together with its eight neighbors, weighs the reds, greens, and blues among them, and assigns the center pixel its final color. On a 50-megapixel sensor that happens fifty million times, faster than you can think about it.
Fujifilm's alternative to the Bayer array. It keeps the green majority but lays the filters out in a larger, less regular pattern, and the irregularity is the point: with no strict grid for the subject's own patterns to drum against, fine weaves and textures cause far less moiré.