[music playing] I want you to stare, really focus on the circle at the center of this group of dots and don't move your eyes.

Do you see it?

If you're not color blind, it's likely you're seeing a blue dot moving around the circle.

Try looking at the blue dot and you'll find it's not there.

Why would your brain tell you something's there when it's really not?

Well, the shocking truth is that this happens to you every day, especially while you're staring at your computer or phone screen.

So in here, I've got some red, and what's the other color?

Green.

Passed the first test.

And I'm going to have you mix it up.

What color do you think it's going to turn?

If I was in second grade, I should remember this, but it should be yellow, right?

Red.

Brown.

Orange.

Purplish.

Purplish.

OK. What is it looking like?

Like a brown, dark red?

All right, what color is it turning?

Greenish brown.

I've got the same color.

It's the same paint, actually, and I'm going to spin it.

What color do you think it's going to appear?

Brown, but I think this is a trick question.

OK, so you're going to say brown again.

You're going to guess brown.

I know it's wrong.

I know it's wrong.

It's a trick question.

It has to be.

I hope this one's yellow and not dookie brown.

OK, you hope this one's yellow.

What color does that look to you?

It looks yellowish.

It's like a mustard yellow.

Like a mustard yellow.

Was it surprising that this kind of dark red and that bright green made yellow?

Yeah, I'm just trying to think of why?

Why is it happening?

Your told in art class that when you mix the three primary colors, red, yellow, and blue, you get brown.

And that's true of paint, but it's not true of light.

When I spin the red and green wheel, there is no yellow light there but you see yellow.

Your brain is being tricked because of how your eyes work.

On your retina, you have light sensitive cells called cones that perceive color, red light, green light, and blue light cones.

Some people have an extra cone which would allow them to see many more colors than the rest of us, which would be crazy.

But typically, we just have the red, green, and blue cones, which means that there is no cone for orange light or yellow light.

But the crazy thing is that these three cones work together to allow you to see the rest of the colors.

It works like this.

If I shine the yellow light on your eyes, your red cones actually respond a little bit and your green cones respond a little bit, too.

Then your brain combines those red and green responses to say that's yellow.

Now, if instead of yellow light, I shine a little red light and a little green light on your eyes, the red cones respond and the green cones respond, and your brain says, red and green, well, that makes yellow-- even if there is no yellow light there.

This is how your LCD screen tricks you into seeing yellow.

It's doing that right now.

All you're seeing with your eyes is red and green, but your brain is seeing yellow, and now blue if you stared long enough at that yellow star.

This is an effect of how your eyes work as well, and so were the yellow dots at the beginning.

They have to do with complimentary colors, but don't get this confused with complimentary or opposite colors on a paint color wheel.

If you mix two of those opposite colors, you get a darker brownish color because adding more pigments means more colors are absorbed.

On a color wheel for a light, mixing two complimentary colors gives you white.

For example, if I show you this red screen and then the cyan screen, and then switch them back and forth fast enough, you should see white.

Here goes.

I really hope that worked, and if it did, you'd be making this face because it's incredible.

You mix two colors and you get white, but white is all the colors.

Or are you perceiving all of the colors?

If I shine red, green, and blue light on your eyes, you're going to see white, because white light excites all three cones just like a mix of red, green, and blue light does.

Otherwise, this wouldn't look white with just the red, green, and blue pixels on your RGB screen.

So red mixed with its opposite color cyan, which is just a mix of green and blue light, should look white.

And now, you'll notice that blue is the complementary color of yellow, so together they should make white.

When you stare at yellow light for a while, your red and green cones continue to respond and eventually become dulled.

When you suddenly switch to a white screen, all three cones should now get excited.

But blue was the only one that wasn't dulled over time, so it will send a stronger signal to your brain and your brain will tell you there's blue light, even when there is not.

But now you know better.

[music playing]