As the concept was explained to me, each color of R, G, and B have a contribution to luminance (that's the detail of the picture, rather than the color of the picture). Green has the most contribution, red has less, and blue has the least contribution of the three.
Human visual perception is based mostly on luminance. This allows us to hunt and gather in very low light, which typically lacks color. The human brain "fills in" the color information we need, which is why we perceive normal color in flourescent rooms that film and digital "see" as greenish.
Our retina is composed of rods and cones. Rods are luminance receptors and cones are chrominance receptors. We have more rods than cones, because seeing shapes is more important to us than the color of those shapes.
The Bayer pattern is nothing more than a design that is actually patterned after human visual perception.