Is the yellow we perceive when our eyes are hit by red and green light at the same time the same yellow that is at the yellow frequency/wavelength? 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?
 A: 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.
A: Because the human eye has sensors that detect only three color bands as pointed out by S. McGrew and MaxW, it is indeed the case that your brain, retina, and optic nerve are wired to tell you that you are seeing "yellow" when there are no photons at all of that energy entering your eye. This effect is called metamerism and is extensively dealt with in the field of physiologic optics.
A: As the other answers state, color perception and frequency of light are two different things. In this plot 


The properties of color which are inherently distinguishable by the human eye are hue, saturation, and brightness. While we know that the spectral colors can be one-to-one correlated with light wavelength, the perception of light with multiple wavelengths is more complicated. It is found that many different combinations of light wavelengths can produce the same perception of color. This can be put in perspective with the CIE chromaticity diagram.

So it is not a simple one to one correspondence.
