Screens mix coloured light additively (RGB) — combining red, green and blue light at full strength produces white. Paint and print mix pigment subtractively — combining pigments removes more of the light spectrum, moving toward black, and print approximates this with the CMYK model. This is the core reason a colour that looks right on screen doesn't automatically translate to the same result in paint.
Practical advice
Treat an on-screen colour as a starting reference, not a guarantee — always confirm the final colour with a physical paint or print sample.
| Pair | Added as light | As filters in series |
|---|---|---|
| Red + green | #FFFF00 | #000000 |
| Green + blue | #00FFFF | #000000 |
| Blue + red | #FF00FF | #000000 |
| Cyan + yellow | #FFFFFF | #00FF00 |
| Magenta + yellow | #FFFFFF | #FF0000 |
| Cyan + magenta | #FFFFFF | #0000FF |
Red and green light add to #FFFF00, a full yellow, while a red filter over a green one passes nothing at all. Cyan and yellow do the reverse: as light they add to white, and as filters they leave #00FF00, a pure green. The additive primaries are the subtractive secondaries, and the other way round.
How this was calculated. Each colour is converted to linear light. 'Added as light' sums the two and clips at the display maximum; 'as filters' multiplies the two channel by channel, as two ideal filters in series would. The swatches are, in order, the two inputs and the two results.