Jack asked why things are the colors they are, and Bobbie wanted to know too. Here is the answer, built up one experiment at a time.
Everything on a dark panel is something you can drag, tap or switch on. Try it before you read the part underneath.
Experiment 1
Light from the sun or a flashlight looks white. But white light is really every color at once, all traveling together.
A prism is a block of glass with flat sides. Glass bends light, and it bends each color a different amount. So when white light goes through a prism, the colors spread apart.
Red bends the least and violet bends the most, so the order never changes: red, orange, yellow, green, blue, violet. A rainbow in the sky is the same trick. The raindrops are the prisms.
The second prism bends the colors back the other way, and they mix into white again. Isaac Newton tried this about 350 years ago. It showed the colors were in the light all along. The glass doesn't make them. It only sorts them.
Experiment 2
At the back of your eye are millions of tiny color detectors called cones. There are only three kinds. One kind notices red light, one notices green, and one notices blue. Every color you have ever seen is your brain comparing how hard those three are working.
Below is a dark room with a red, a green and a blue spotlight. Drag them around and make them overlap. Tap anywhere to see what your eye gets at that spot.
Drag the lights. Tap a spot to test it.
Tap anywhere on the dark room to see what your eye gets there.
Can you make
All of them. That's what every screen in the house does all day.
Look where red and green overlap: yellow. But there is no yellow light in that room at all. Your red cones and your green cones are both working, and your brain calls that yellow. It can't tell the difference between that and real yellow light.
And brown? Brown is just orange turned down low.
Every color on this screen is made of tiny red, green and blue lights, too small to see one at a time. Pick a color and zoom in.
Yellow on a screen is only red and green lights. White is all three at once. Zoom in close enough and there is no yellow or white in there anywhere.
Experiment 3
A banana doesn't glow. In a dark room you can't see it at all. You only see it when light lands on it and bounces off into your eyes.
Here is the secret: everything swallows some colors and bounces the rest. The colors that bounce off are the colors you see. Pick something to shine white light on.
Real light has thousands of colors in it, not just three. Three is enough to see how it works, and it's how your eyes sort them anyway.
Experiment 4
If the color you see is only the light that bounces back, then changing the light should change the color. This is a dark room with black cloth on the table. Pick a flashlight, then tap anything on the table to find out what is happening to it.
Tap something on the table.
Can you
So what color is a banana in the dark? It doesn't have one. The color isn't inside the banana. It's what happens when light, the banana and your eyes all meet.
Experiment 5
Shine red and green light together and you get yellow. Mix red and green paint and you get a muddy brown. Why?
Light adds. Every light you switch on gives your eyes more. Paint takes away. Each paint swallows some colors, and every paint you mix in swallows more, until hardly anything bounces back.
These are three see-through colored sheets on a light box. Each one swallows one color. Drag them on top of each other.
Drag the sheets. Tap a spot to test it.
Tap anywhere on the light box to see what light gets through there.
Can you make
Yellow swallows blue. Sky blue swallows red. Put them together and they swallow blue and red, so only green gets through.
Printers use exactly these three inks, sky blue, pink and yellow, because ink works by swallowing. Screens use red, green and blue, because screens make light.
Experiment 6
Air is made of tiny bits, far too small to see, and they knock light around. They knock blue around much more than red. So as sunlight comes down through the air, some of its blue gets bounced sideways, again and again, until it is coming at you from every part of the sky. That's the blue you see when you look up.
Now move the sun down towards sunset.
How much of each color gets through the air to you
At sunset the sunlight takes a long, slanting path through the air to reach you. Almost all of its blue gets knocked out along the way, and most of the green too. What's left is orange and red, so that's the color of the sun and the sky around it.
Never look straight at the sun, even at sunset. And why isn't the sky purple, when violet gets knocked around even more than blue? Sunlight has less violet in it to begin with, and your eyes are not very good at seeing violet. So blue wins.
Experiment 7
Color isn't inside things. It's what happens when light, a thing, and your eyes all meet.