It only looks plain. Send it through a prism and the disguise falls away — out fans a whole rainbow that was hiding inside the whole time.
Unmask the lightThe "white" light pouring from the Sun, a lamp, or your screen is not one colour at all. It is every colour blended together — and a prism or a raindrop can pull that blend back apart into a rainbow.
So colour isn't something painted onto the world. It is a story about which colours of light reach your eyes — which ones bounce off a thing toward you, and which ones get soaked up and never make it. Once you see light that way, a prism, a rainbow, and a plain red apple all turn out to be the same trick told three ways. You're about to play with all three.
Here is the idea that flips everything around: white light is not a colour of its own. It is a crowd — red, orange, yellow, green, blue, and violet light, all travelling together and mixed so smoothly that your eye reads the whole blend as plain white. Think of it like a smoothie. Once it's blended you can't pick out the strawberry from the banana from the kiwi by looking, but every one of them is still in the glass.
That full spread of colours, laid out in order, has a name: the spectrum — just "the range of colours that light comes in." White light contains the whole spectrum at once. Most of the time the colours stay perfectly mixed and you never notice them. But there's a way to un-blend the smoothie, to spread the crowd out so you can see every member: send the light through a triangle of glass called a prism.
A prism doesn't paint colours onto the light or add anything to it. It simply separates the colours that were already there, fanning them out so they stop overlapping. White goes in one side; a rainbow comes out the other. The colours were inside the beam the whole time — the prism just gave them room to spread. Let's watch it happen, and let you move the beam around yourself.
A single white beam streams in from the left and strikes the prism. Slide to aim the beam up and down, or tilt the prism, and watch the rainbow swing. The colours leave in a fixed order, every single time — that order is the spectrum.
White light enters the glass, and because each colour bends by a slightly different amount, it leaves fanned into a spectrum. (The spread is widened a little here so it's easy to see.)
Why does the white beam break apart at all? It comes down to bending. When light crosses from air into glass it slows down a touch and bends — and the lovely twist is that each colour bends by a slightly different amount. Violet bends the most, red the least, and the others spread out in between. One bend going in, another coming out, and that tiny difference gets stretched until the colours separate into a fan you can actually see. The prism never added a thing; it just bent each hidden colour by its own amount.
Look closely at the fan and you'll notice the colours never shuffle. They always come out in the same order, because each one always bends by the same amount. From the side that bends least to the side that bends most, the order is:
Indigo is the deep blue-purple squeezed between blue and violet. It was added centuries ago to round the list out to seven, and your eye can find it tucked in there — but don't worry if blue and indigo look almost like twins to you. They very nearly are.
This is the same order you see in a real rainbow in the sky: red on the outside of the arc, violet on the inside, with the others stacked neatly in between. That is not a coincidence — and it points straight at where rainbows come from.
A rainbow looks like magic painted across the sky, but it is really the prism trick blown up enormous — with raindrops doing the prism's job. Each tiny, round drop of rain acts like a miniature prism: sunlight goes in, bends and splits into colours, bounces once off the back inside of the drop, and bends again on its way back out. Every drop sends the colours back to you spread into a little fan.
A single drop only sends one colour toward your eyes from any given spot — but the sky after a shower is full of millions of drops at every height. Together they hand you the whole spectrum at once, stacked into that giant curved arc. Red reaches you from the drops up high, violet from the drops lower down, and the rest fill in between. Millions of tiny splitters, one grand rainbow.
A rainbow always sits in the part of the sky opposite the Sun — so on a sunny, drizzly day, stand with the Sun behind your back and look toward the rain. That's also why you can make your own with a garden hose on a bright day: spray a fine mist with the Sun behind you, and your private rainbow appears. The water drops are the prism; you just have to stand in the right spot.
So a rainbow isn't a thing hanging in the air that you could walk up to and touch. It is light, split by water and bent back toward your eyes from exactly the right angle. Step sideways and it shifts with you, because it was always built just for where you're standing.
Now the big question: if white light is every colour mixed together, why isn't everything just white? Why is grass green and a strawberry red? The answer is the heart of this whole page, and it's beautifully simple.
When white light — the full crowd of colours — lands on an object, the object doesn't bounce all of it back. It reflects some colours and absorbs the rest. To reflect means to bounce the light away; to absorb means to soak it up, so it turns into a little warmth and never reaches your eyes. The colour you see is simply the light that bounced off and made it to you.
So the colour was never really in the strawberry the way its sweetness or its seeds are. The strawberry is just very good at bouncing red light and very good at swallowing the rest. Change the light you shine on it, and you can change the colour you see — which is exactly what the next toy lets you do.
Choose what colour of light to shine, and toggle which colours the object is able to reflect. Watch what reaches the eye. Start with the red apple under white light, then switch the light to green and see what happens.
White light has every colour. The object reflects only red and soaks up the rest, so you see red.
Notice the rule the toy is following: you only see a colour if it is both in the light AND something the object can reflect. A red apple under white light looks red because white light contains red and the apple bounces it back. But shine pure green light on that same apple and it has no red to bounce — and it can't reflect green — so nothing comes back to your eyes and the apple looks black. It didn't change at all. You just stopped giving it the colour it needs.
That black apple is the moment the whole idea clicks. An object's colour is a conversation between the light and the object — and if you change either side of the conversation, the colour changes too.
You've probably seen this for real without naming it. Under the warm orange glow of a sunset, white walls turn peachy. Under the harsh blue-white of a phone torch, skin looks paler and colder. In a shop with reddish lighting, blue jeans can look almost grey — because there isn't much blue light around for them to reflect. Stage and disco lights use this on purpose: bathe a scene in deep red light and the blues and greens go dark and muddy, because the light simply doesn't carry the colours they'd need to glow.
This is why artists, photographers, and even shops care so much about their lighting. To judge a colour honestly you need white light — the full crowd — so that every colour an object could reflect actually has the chance to. Take away part of the spectrum, and you take away part of what anything can show you. The object holds up its end of the deal; the light has to hold up the other.
Here's something that surprises almost everyone. In art class you learn that mixing more and more paint together gets you a muddy brown, heading toward black. But mixing more and more light together does the opposite — it gets brighter, heading toward white. Same word, "mixing," two opposite directions. Why?
It comes straight from reflecting versus absorbing. Paint mixing takes colours away. Each blob of paint works by absorbing some colours and reflecting the rest; pile two paints together and between them they absorb even more, so less light escapes and the mix turns darker. Light mixing piles colours on. Shine a red beam and a green beam onto the same white spot and now both bounce back to your eye together — your brain blends them into yellow. Add a third, and you fill the spectrum back in.
Three beams of light — red, green, blue — overlapping. Where all three pile up, you get white.
That's why screens glow with tiny red, green, and blue dots. With just those three colours of light, turned up in different amounts, a screen can mix nearly every colour you've ever seen — and switch all three to full to make white. Your TV, your phone, your tablet: every picture on them is light being added together, the exact opposite of a paintbox. Keep the two kinds of mixing in separate drawers in your head and you'll never get them muddled.
You now understand colour better than most grown-ups. Here are the two slips people make most often — and spotting them is the surest sign the idea has really landed.
An apple is red the way it is round and sweet — the redness lives in the apple, glued on like a coat of paint.
The apple has no colour sitting inside it waiting to be seen. It only has a habit: it bounces back red light and swallows the rest. The colour happens out in the open, in the meeting between the light and the apple and your eye. Take the red light away and the "red" vanishes — proof it was never locked inside the apple at all.
White light is plain and colourless, and the prism is a clever paintbox that creates a rainbow and stains the beam with colour.
The prism doesn't add a single colour. Every colour was already hiding inside the white beam, perfectly mixed. All the prism does is bend each one by its own amount, so they spread apart far enough for you to see them one by one. It's an un-mixer, not a paintbox — and a second prism can even catch the fan and blend it back into white.
Both slips come from the same habit: thinking of white as "no colour" and of objects as "owning" their colour. Flip both around — white is all the colours, and an object only borrows the ones it bounces — and every puzzle on this page solves itself.
See if it's all clicked into place. Tap an answer to reveal why.
White light is every colour mixed together — red through violet, the whole spectrum at once.
Each colour bends by its own amount, so a prism or a raindrop fans them into a rainbow. Nothing is added.
A thing looks coloured because it reflects some colours and absorbs the rest — so colour lives in the light, not the object.