This is another old one, from May 31, 2007. I love this idea a lot.
Let us say, hypothetically, that at birth, you were born with an undetectable case of what doctors would eventually come to call “Photo Negative Colorblindness.” You perceive colors as the exact opposite of what they really are, but you have no idea you have this ailment because you were taught that the color that everyone calls green was really seen as the color red. For instance, when you were young, your parents would point to a red object, and call it red. However, due to your illness, you perceive that color as green, but still call it red.
So the average person, when looking at Figure 1, would see a red rectangle with a blue circle, but if you had “PNC,” when looking at Figure 1, you would see Figure 2 instead. You would still call Figure 2 a red rectangle with a blue circle, but you would unknowingly be looking at what truly is a green rectangle with a purple circle.
Some people begin to question life when I explain this to them