How would you describe the idea of a colour to a person blind from birth?

 

  I sit him or her down with my arm around the shoulders and explain, “Here, we’ll start by you taking a bite of this sandwich, chew it slowly, and then we’ll discuss what you think the different tastes look like . . . ”

(Meh, I’ve never claimed to be any kind of research scientist for cognitive relativity! Grrrrrrr.)
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I might start by having the person feel cold (water) with their hand and say cold is related to blue color and similarly hot relates to red color. Then try think of how to relate the different colors to different sounds or something. At least experiment with different ideas see what might work for the person.