> I read about an experiment where people were shown various black and white drawings over random grayish backgrounds. They then had to estimate the hue of the grayish background - which was tricking because it only has slight amount of red, or blue, etc)

I'm colour blind, and if a picture is in black and white, I can't always tell.

A long while back our CRT TV broke, and started displaying everything without colour - I had no idea until my wife pointed it out! It's like my mind just makes up what it doesn't see.

Another example that I always use is grass: if you showed me a cropped image of grass and I didn't know it was grass, I'll tell you "I don't know what colour it is, but I think it's either red, brown or green". But if you point to some grass, I'll always say "it's green!".