I make no claim to special insights into color matters, but the friction between Jani and Bill Janes makes me think there's something of interest to be resolved here.
Why should a red and green light, mixed together, produce yellow? Off the top of my head, I would say, because the shorter wave lengths of red are yellow and the longer wavelengths of green are also yellow. Combine them both and you get a reinforcement of the frequencies in common which produce the sensation of yellow in our minds.
Yet, doing some Googling research on the matter, I came across the following reference from the most amazing of all encyclopedias, Wikipedia, which is in a constant state of revision and correction by anyone who thinks he has the knowledge. (Great concept!)
As you will see from the above image, there is no overlap between the red and green frequencies, so the question arises, if red and green light with the exact frequencies as shown in the Wikipedia image were superimposed, or mixed, would yellow result? If so, how?