VERIFIED · 01.10.2026 AI help: yes reviewed by: teacher and psychologist · 2026-10-01

Colours and Screens

A phone screen shows millions of colours. Yet inside there are only three colours of light. Today you will see how all the others are made.

⏱ 10–15 min Explorer Inside the Computer · 8 grades 4–5

You will be able to name the three lights in a screen, predict which colour their mixture makes, and read a colour written as three numbers.

For parents: a one-page guide — dinner questions and an activity without a screen.

01Remember

Three questions from earlier lessons. Think first, then open the answer.

What is a pixel?

The smallest dot of the picture on a screen. The picture is made of many such dots arranged in rows.

How many states does one bit have?

Two: on and off. We write them as 1 and 0.

Is a screen input or output?

Output — it shows us the result. (A touchscreen is also input, because we touch it.)

02Story

In 1861, the photographer Thomas Sutton took the first colour photograph. He made it for a lecture by the scientist James Clerk Maxwell. The subject was a ribbon with a checked pattern.

There was one problem: the camera was black and white. So Sutton photographed the ribbon three times — through a red, a green and a blue filter.

Then the three black-and-white pictures were shown with three projectors. Each one had the same coloured filter that was used to take its picture. When the beams overlapped on the screen, a colour picture appeared.

Maxwell had suggested the idea — making colour from red, green and blue — in 1855. Your screen does the same today, only much smaller and much faster.

03Worked example: how to make yellow

There is no yellow paint in a screen. Yellow is made like this:

Three lights
Every dot of a screen can shine red, green and blue. That is why it is called RGB.
Three numbers
The computer says how strongly each light shines — with a number from 0 (off) to 255 (strongest). Yellow is (255, 255, 0): red at full, green at full, blue off.
Lights add up
Red and green light shone together add up. Our eyes see yellow. Light mixes differently from paint — you will try that in “No screen”.
Many colours
Each of the three lights has 256 steps (0 to 255). Together that makes more than 16 million different colours.

RED255

GREEN255

BLUE0

= YELLOW(255, 255, 0)

04Try it

1 · Predict

Red and green light shine together. Which colour will you see? Choose before you check.

2 · Run: the light mixer

Move the sliders. Each one is a light from 0 to 255. Or press a ready-made button.

Red0 Green0 Blue0

The colour as numbers: (0, 0, 0)

✋

Be sensible with screens

Do not look at a screen from very close for long. After a few minutes, look out of the window at something far away. Never put anything wet on a device.

3 · Change: the magnifier and the challenge

Press “Turn the magnifier on”. The drawing shows how a few pixels look under a magnifier: each one has three little lights. Change the numbers and watch the little lights get stronger or weaker.

Challenge: make orange. Hint: more red, less green, no blue.

05No screen: lights and a magnifier

You need: a magnifying glass, a phone or tablet, and an adult next to you.

Ask the adult to open a big white or yellow patch on the phone and set the brightness to medium.
Look at the screen through the magnifier for a few seconds. Do not press the glass against the screen. On many screens you will see rows of tiny dots or little stripes in different colours. On some screens they are hard to see — that is normal.
Put the magnifier down and look out of the window at something far away to rest your eyes.
On paper, paint a red patch and a green patch that overlap. What colour appears where they overlap? Is it the same as with lights?

✋

Magnifier — only on a screen

Never point a magnifier at the sun or at a bright lamp. Never look through it at a light.

06Make your own

Make your own colour map.

Draw 6 squares in colours you like.
Under each one, choose three numbers from 0 to 255 — the way you think a computer would say it.
Check in the mixer above. How close are you? Fix the numbers and try again.

07What I learned

A screen makes its colours from three lights: red, green and blue (RGB).
Every colour is three numbers from 0 to 255. Red + green = yellow, all three = white, none = black.
A pixel is the smallest dot of the picture. From a normal distance, our eyes blend its little lights into one colour.

A computer describes every colour with three numbers. How would you describe a colour to someone who cannot see it?

Check yourself

1. Red and green light shone together make…

black yellow brown

2. Which are the three colours of light in a screen?

red, green, blue red, yellow, blue white, black, grey

3. What do you get if all three shine at full strength (255, 255, 255)?

black brown white

Skill badge: “I mix colours with light”
It is yours when you can explain to someone how a screen makes yellow and white. No points and no rankings — just a skill.

08I have a question

Do you still have a question? Write it here. It goes to your parent, not to strangers. Your parent confirms their e-mail first.

The form is loading… If it does not appear, write your question on paper and show it to a parent or teacher.

·Sources

Title: Colours and Screens (DB-VK-08) · Author: Children's Library, East Accelerator Foundation · Source: original content, 2026 · Rights: CC BY-SA 4.0.
Facts checked on 01.10.2026 (links only, no text copied): Wikipedia, “Additive color” · “RGB color model” · “Color photography”.
School link: Bulgarian curriculum, Computer Modelling and IT, grade 5 — graphics (Ministry of Education programme, in Bulgarian, checked 01.10.2026).
Licence: CC BY-SA 4.0 · Children's Library, East Accelerator Foundation, 2026. You may share and adapt this lesson if you credit the author and keep the same licence. Learning is free forever.