The RGB color model has its origin in physiology, to match the three types of color receptors in our eyes.
(The LAB color model also originates from physiological considerations, but on the neurological level, i.e. at least one step after the color receptors.)
RGB doesn't really match the color receptors though. The cones in your eyes are more like 'blue', 'yellow-green', and 'yellow-red'. RGB is just a convenient way of covering a decent amount of the color space we can perceive.
Take a look at the LAB color model. It's defined with three axes; lightness, green–red and blue–yellow.
Yellow has no special meaning in this model.