Color mixing simulator

What this simulator shows

There are two ways colors mix. In Light mode, three spotlights shine red, green and blue onto a dark wall, and where they overlap the light adds up. In Paint mode, three circles of cyan, magenta and yellow ink overlap on white paper, and where they overlap each ink takes away more light. Each color has an on/off switch and a slider, and the readout names the color in the middle, where everything that is switched on overlaps.

• Adding light: red + green = yellow, green + blue = cyan, red + blue = magenta, and all three = white.
• Mixing inks: cyan + yellow = green, magenta + yellow = red, cyan + magenta = blue, and all three = nearly black.
• Screens make every color from tiny red, green and blue dots. Printers use cyan, magenta and yellow ink, plus black.

Why the two modes are different

White light contains all the colors. A spotlight adds its color to the wall, so more lights mean more light reaching your eye, and overlaps get brighter. An ink works the other way: it absorbs some colors from the white light shining on the page and reflects the rest. Cyan ink absorbs red, magenta absorbs green and yellow absorbs blue. Stack them and less light gets reflected, so overlaps get darker. Seeing both side by side, with the same kind of controls, makes the difference clear.

Common misconceptions

Children are usually taught that the primary colors are red, yellow and blue, so red, green and blue lights making yellow and white comes as a big surprise. Red, yellow and blue is a traditional painters' set; scientists and printers use red, green and blue for light and cyan, magenta and yellow for ink. Another common idea is that mixing all colors of light makes black or brown, as it does with paint. A third is that a yellow on a screen contains yellow light. It doesn't: it is red and green light that your eyes read as yellow. The paint mode uses ideal printer inks; real paints are less pure, so real mixes look duller.

A 10-minute color activity

• Ask: "What do you get if you mix red and green?" Write down the answer.
• In Light mode, switch blue off and look at the middle. Talk about the surprise.
• Try the other two pairs, then all three. Ask the child to make a quick table.
• Switch to Paint mode and repeat. Compare the two tables.
• If you have a magnifying glass, look closely at a white area of a screen to see the colored dots.

Where this fits in school

• US, middle school: NGSS MS-PS4-2 asks students to model how light is reflected, absorbed or transmitted by materials, which explains why inks and objects have color.
• England, Key Stage 3: pupils study colors and the different frequencies of light, white light and prisms, and how colored objects absorb and reflect light differently.
• Younger children enjoy the light mode as a first look at color, alongside art lessons on mixing paint.

Learning more

Light and color are part of Eurekami's science skill map, with lessons that build up diagrams live and explain each step. A few daily practice questions help the color rules stick.