This is a great question because it concerns a basic problem in studying behavior—how do we know what others perceive? When you, or I, or a dog, look at an object, are we actually experiencing the same thing? The short answer is that there is no way to be sure. You and I can point at things and ask whether we would both call that color red, but that doesn’t mean we see the same thing. We can train a dog to pick a red ball instead of a blue one, but that does not mean the dog sees the colors the way we do.

If you want to see whether you and your friends may have trouble seeing specific colors, there are a lot of online tests. Here’s one at:

The reason they use a bunch of circles with different shades is because there are several cues when a color is different. A color could be darker or lighter (use more ink, for example) or have more black or white added to it. When colorblind children are learning their colors, they may be using these cues. For example, the teacher’s green circle may be darker than the red one. They learn to call the darker color green. The most common form of color blindness is the form when people can’t tell red from green. This problem is much more common in males.

If you want to see what the test would look like to a colorblind person, adjust your monitor to black and white or make a black and white printout of the test.

If you often wonder about how others see the world, you might be interested in studying psychology.

This is a great question that I thought about for a long time. For example, you could give people the entire range of colors and ask them to find the “bluest blue” with no green or purple and see if they choose they all choose the same color. If they choose different colors then you know that they are seeing colors differently. If they all agree on almost the same color then you know that they all think of “blue” as the same thing, but you still don’t know if they are seeing the same thing. Our eyes see color with special “cones” that detect the wavelengths of red, green, and blue light. By mixing those we can see all of the other colors. Each person has a different number of red, green, and blue cones, which suggest that people do see color differently, even if they agree on what the colors are. To check this hypothesis, you need to look at the signal that the eyes send the brain for different colors and then compare people with different numbers of red, green, and blue cones.

Honestly, you can't, at least with our current technology. We don't have a way to monitor what a person is thinking or experiencing at this time.

Personally, I hope we never have that. Consider how dangerous it would be..