The other question that occupied me many times is what color is seen by different people. For instance, assume your eyes are 'perfect' and I have a weird genet

The other question that occupied me many times is what color is seen by different people. For instance, assume your eyes are 'perfect' and I have a weird genetic color perception problem: I've learned that grass is 'green' since childhood. So I call the color of grass 'green' even though I might perceive that color the same way you perceive the color of a ripe tomato. To me your 'color of a ripe tomato' is a color I've always called 'green', so you and I will still call that color 'green', even though the color I actually see with my eyes is your 'red'. We can never know what the other's color perception is.