Colour Mixer

Red and green paint make a muddy brown, but red and green light make yellow! Shine three coloured spotlights, then try paint, and see why they're different.

Mix
Colour at the probe
White
RGB
255, 255, 255
Hex code
#FFFFFF
Mixing
All three

The maths, live

Light adds up R + G + B(255,0,0) + (0,255,0) + (0,0,255) = (255,255,255)
Red + green = yellow, all three = whiteEach value is capped at 255

Move the probe into each overlap. Which two lights make yellow? Now switch to paint: which two paints make blue?

How it works

Mixing light is adding. Your eyes have sensors for red, green and blue light, so a screen makes every colour from tiny red, green and blue dots. Red + green = yellow, green + blue = cyan, red + blue = magenta, and all three make white.

Mixing paint is taking away. White light hits the paper, and each paint soaks up (absorbs) part of it. Cyan absorbs red, magenta absorbs green and yellow absorbs blue. Cyan + yellow leaves only green; all three absorb everything, leaving black. Printers use these colours for this reason.

Try this

  1. Which two lights make yellow? Can you make orange?
  2. Turn the blue light down. What happens to the white middle?
  3. In paint mode, which two paints make blue?