I am trying to understand how color works, and I am curious whether the yellow we perceive when our eyes are hit by red and green light at the same time is the same yellow that is at the exact yellow frequency.
What I mean is that I read recently that white does not have a frequency by itself, but rather that we perceive white when we perceive all frequencies of light at once(at least ones we are sensitive to).
What confuses me is that based on Wikipedia chart, 
red has a frequency of ~480, and green has a frequency of ~550, whereas yellow has a frequency of ~540. So i am not sure whether they add up in some way to become equivelent to yellow, or if the presence of red and green makes our eyes perceive yellow without there being any yellow.
To clarify, I mean that yellow has its own frequency and wavelength, and red and green have their own frequencies and wavelengths, so when we see yellow, is it equivalent to seeing red and green, or can we perceive red and green but if we capture the frequency of yellow of the light, there may not necessarily be any yellow there. Also, if they are different yellows, then what happens if red, green, and yellow is present at the same time?
Best Answer
Great question. This page (https://en.wikipedia.org/wiki/Color_vision) indicates that there are three cones in the human eye which absorb and hence are sensitive to different areas of the spectrum. Our metal perception of colour is then a ratio of what is being received by these cones. By mixing red and green, yellow is perceived not because a yellow frequency is produced by mixing or beating, but because if you get the ratio right it activates the cones in the eye in the same way as yellow would. This isn't a full answer because I don't understand it fully. It looks like it's more a biology question than a physics one - hopefully digging into colour vision will answer it fully.