Colours

I think about colours a lot. I remember learning in science when I was younger about how colours are not real, how they are just reflections of light. Then I think about blind people. Not people who were in an accident as a child, but blind from birth people. Say you took one out to a field, they could feel the grass, its shape and texture and they would understand what it looked like from that, but then you would tell them that this grass is green. What would they picture in there minds? If colours are just reflections of light, and a blind person can never see light, then do they just picture things in black and white? Or does there mind create colours that are impossible for even us to imagine because our imagination is so limited by what we know?

How would you describe a particular colour to somebody? Can it be done?