I think your question is about the perception of colour - ie how your brain responds to the mixture of light which stimulates the retina. This cannot be explained by the superposition of waves using Maxwell's equations. It is more a matter of physiology (biology) than physics .
Colour is not a property of the physical world. It is our subjective response to the different frequencies of light which stimulate the retina. Different combinations of stimuli result in different 'colours'. While the individual colours in the visible spectrum can be identified with different frequencies of light, the eye/brain can "see" many more colours which are not found in the visible spectrum of light.
Not everyone has exactly the same colour-response to the same combination of frequencies - even allowing for colour-blindness. The colour recorded by digital cameras or photographic film can likewise be different from what is seen with the naked eye.
Contrast and resolution are important factors in determining whether the eye can distinguish adjacent patches of different colour. The smaller the angle they subtend, or the closer the two colours are in the Colour Triangle , the harder to recognise them as two separate regions of distinct colour.
When your eye is unable to resolve the individual patches of different colours in an object, then the brain does, as you suggest, interpret some kind of an average colour. You see this effect in an Art Gallery in pointillist paintings. Up close the painting is nothing but a confusing forest of distinct blobs of paint of different colours. When you are far enough away your brain 'averages out' the differences and interprets a single colour (as well as distinct features, such as human faces and expressions).
You get a similar effect in Maxwell's Colour Wheel. When a wheel painted in a combination of colours is spun so fast that you cannot focus on any one colour, your brain interprets a single colour approaching white.
In response to your comments below :
I must say that I agree with the "renowned person on IRC" : I do not understand what point you are trying to make about the "sum of plane waves". It does not seem to have any significance for the problem you describe in the 1st paragraph of your question.
The individual leaves in the Amazon forest are not each a distinct pure shade of green with a definite frequency in the EM spectrum. Most of these greens are mixtures of many different frequencies corresponding to pure yellows and blues from the EM spectrum, as well as greens and perhaps reds also. See the Colour Triangle in  which explains that
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.
The superposition of waves of definite frequencies does not create new colours in the light which enters the eye. The different shades of green which we "see" are created in the brain. Mixing light is not the same as mixing paints of different colours.
It seems to me that you really want somebody to tell you that you are right and the "renowned person" was wrong about a distinction which you are trying to make. I am not sure that I understand what that distinction is, but it seems to me either wrong or insignificant.