How do you know if someone else sees colors the same way you do?

Question

For example, isn't it possible for someone to see the color red in a slight different shade, or maybe totally different color, than everyone else? But to them, it's still red because that's what they've known that color by their whole life.

Answer 1

Get them to take a colorblind test with you!

Answer 2

You don't. And the same is true for any other sensation: smell, taste, sound, etc. The perception is a process that is internal to the brain, and until we find a way of capturing a sensation and transpose it into someone else's brain (through some yet to be invented process) we will not know.

But the sensation (whatever it is) of seeing red is reliably associated with the presence of a (objective) red color. No one (except for people with color blindness) would mistake red for blue and call it so, under normal conditions.

Answer 3

You dont, thats why its called 'philosophy'