“What about red-orange?”, you say.   “Red-orange light would also simultaneously  stimulate the Red and Green receptors.  See?”
			Aaahhh…..true. But look!  The relative lengths of the arrows are different. The green arrow, i.e. G-receptor, is much less stimulated than the R -receptor.
				So, red-orange light is seen as different from yellow light due to the ratio of R and G response.