Mixing Light vs Mixing Paint

Lesson 8 of 10 · 7 min · Free, no account needed

What you will learn

Additive colour: light adds. Red + green = yellow, green + blue = cyan, red + blue = magenta, all three = white.
Every colour on a screen is three numbers: how bright the red, green and blue subpixels glow (0 to 255).
Subtractive colour: paints and filters take colours away. Mixing paints absorbs more, so the mix gets darker.

Zoom into the yellow part of your screen with a water drop. What will you see?
Three spotlights: red, green, blue. Overlap them.
Any colour from three numbers. Make yellow, then orange.
Additive and subtractive colour.
Additive colour (light): adding colours of light makes brighter colours. Red, green and blue are the primaries; all three make white.
Your eye has three kinds of colour sensors, roughly for red, green and blue. That is why three lights can fool it into seeing any colour.
Subtractive colour (paint, ink, filters): each one absorbs some colours and passes or reflects the rest. A colour filter lets one band through.
Simplified: real paints reflect a broad mix of wavelengths. We model each paint as three numbers that multiply.
Game: Colour match. Five shades, three sliders.
Your score is how close you get, shade by shade.
Now mix the same colours as paint.
Code: a pixel is a list of three numbers.
A screen pixel has a red, a green and a blue part. Yellow light is red plus green with no blue, so the list is [255, 255, 0]: the first number is red, the second green, the third blue.
This pixel must show cyan. Which subpixels glow?
In additive mixing, cyan is what you get from green light plus blue light. Red stays off: adding red would turn it white.
Your palette on a phone screen. Zoom in.

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