Post Praetorian said:

imperialscum said:

Is the radiation with frequency of 650THz (blue colour) decoded the same way in brain between different people? Could it be that what is my brain's blue is your brain's red? But we all call it blue because that is how we were taught by parents looking at the same object, while in fact experiencing a different thing in our brain.

It is possible, however such a concept is unlikely given the universal acceptance of color groupings such as fall colors, pastels, jewel tones, etc. Further, if my sky were red instead of blue my sunsets would be much less spectacular. My sunsets are spectacular therefor the sky cannot be red.

Alternately, how might one describe a color one cannot see?

I don't think you understood the problem. The name of the colour is standardised based on the frequency of radiation emitted by some common and distinct objects in the nature. Why do you call the sky blue? Not because of what you experienced inside your brain but because someone told you that the sky is blue. So only after that you associated your brain perception to what you were being taught. However brain perception of sky can be different from person to person and yet we will all call it blue because that is how we were being taught and because the radiation frequency is universal.

Same with the fall colours, as you gave the example. We were told that the leafs are red and yellow in autumn. And we have no problem calling it red and yellow despite possible different brain perceptions. This is simply because we associated our different brain perception to the particular frequency of radiation, which is universal.