Light and pigment: why screen and canvas disagree

On a screen, anything seems possible: a neon green , a blazing cyan , a glowing pink . Then you open your tubes and cannot get there. You are not clumsy: a screen and paint do not make colour the same way.

A screen adds light

Look at a screen very closely: each dot is made of three tiny lights, one red , one green , one blue . To make yellow , the screen lights the red and the green. For white, it lights all three. The more lights it turns on, the lighter the colour. A screen adds light.

Paint takes light away

Paint gives out no light at all. It receives the light of the room, which holds every colour of the rainbow, and absorbs part of it. Whatever it does not absorb comes back to your eye: that is its colour. A yellow mostly absorbs blue. A blue mostly absorbs red, orange and yellow.

A screen is a lamp; paint is more like a filter: it only takes light away. In a mix, each pigment keeps absorbing its share. For each colour of the rainbow, the mix sends back an amount between those of the two tubes, often closer to the tube that sends back less. That is why a mix is often darker and duller than you expect. To make a colour truly lighter, add white or a lighter tube.

Screen colours that paint cannot reach

A screen can turn its green fully on, and nothing else. No pigment sends back that much green while absorbing everything else. This pure green stays out of reach of any tube, whatever you mix.

The screen’s green

A screen can light up a pure green. Here is the closest green a yellow and a blue can give.

On the screen

This green is made of light: the screen turns its green dots fully on, and nothing else.

In paint

The greenest green Hansa yellow and phthalo blue can give. Difference from the screen green: ΔE 34. Above 6, they are already two different colours.

Your tubes are not to blame. Painters have always known it: a canvas cannot glow like a lamp. To make a green look brilliant, they surround it with duller or darker colours.

Mixing is not averaging

Many drawing apps mix two colours by averaging their RGB codes: the three numbers, red, green and blue, that tell the screen how much to light each of its three lights. The average of a pure yellow and a pure blue is then grey: it is the average of two lights.

In paint, yellow and blue give green →. Yellow absorbs blue and violet; blue absorbs red, orange and yellow. What neither of them absorbs is green: that is what comes back to your eye. Tubomix works out mixes the way paint behaves, not the way light does.

Yellow + blue, with no grey on the way

Slide from the yellow to the blue. On the right, the colour to reach: a jade green.

Hansa yellowPhthalo blue

Hansa yellow, straight from the tube: pale bright yellow (value 9). Next to the colour wanted: too light, too bright and a different hue.

As you slide, notice two things. First, the mix goes through yellow-greens and then bright greens, never through grey. Second, with these two tubes alone, the jade green you are aiming for  stays out of reach: the mix is always too dark. It needs white: that is the “Your turn” exercise at the bottom of this page.

To remember

• A screen adds light; paint takes it away.
• A paint mix is often darker and duller than you expect.
• To make a colour truly lighter, add white or a lighter tube.
• In paint, yellow and blue give green; an average of screen colours gives grey.
• Some very bright screen colours do not exist in paint: Tubomix tells you so, and offers the closest one.

Further reading

• Additive colour and subtractive colour: the two ways of making a colour, on Wikipedia.
• Gamut: the range of colours a screen, a printer or a box of tubes can produce, on Wikipedia.
• Additive & subtractive color mixing: Bruce MacEvoy explains to painters why paint does not mix like light.
• How Tubomix works (lesson 8): how the site works out a paint mix.