my reasoning: the actual colors we can see -> the wavelengths that we can extrapolate to -> basically extrapolated wavelengths plus an 'unpure-ness' factor -> not even real wavelengths (ok well king blue and maybe lavender if I'm being generous could be)
All receptors are always triggered for all wavelengths we can see, just some more than others. Different color have different ratios. An exactly 540 nm green light would still trigger all 3. It is all your brain doing the processing and those 3 primary colors of our usually 3 cone cells are the opposite of spectrally pure. Otherwise you would not even be able to see those mixed colors.