The particular white a colour space, display or viewing condition treats as neutral.
Specified as a chromaticity, usually that of a CIE standard illuminant: D65 for sRGB, Display P3 and most video; D50 for print and ICC profile connection.
A white point is not a brightness setting. Two displays at the same brightness with different white points show every colour differently.
Evening 'warm' screen modes move the display's white point towards yellow.
Converting between a D65 space and a D50 workflow without adapting the white point shifts every colour slightly warm or cool.
A white point is a chromaticity: a pair of x, y coordinates on the CIE diagram, or the equivalent XYZ values. For a display it is measured by showing full white and reading it with a colorimeter. For a viewing environment it is the chromaticity of the light on a perfect white surface. The usual names are shorthand for particular pairs: D65 and D50 are points on the CIE daylight curve near 6,500 K and 5,000 K.
| Treatment | L* | a* | b* |
|---|---|---|---|
| D65 white read straight against D50 | 100.0 | −2.4 | −19.4 |
| D65 white adapted to D50 first | 100.0 | 0.0 | 0.0 |
D65 has chromaticity 0.3127, 0.3290 (about 6500 K) and D50 has 0.3457, 0.3585 (about 5000 K). Skip the adaptation step and screen white comes out with a b* of −19.4, a distinct blue, instead of the neutral it is. Every other colour in the image carries the same error.
How this was calculated: sRGB white is converted to XYZ, then to CIELAB relative to D50, once directly and once after Bradford chromatic adaptation, the transform ICC colour management uses.
A print is compared with its on-screen proof, the screen at D65 and the print under a desk lamp.
The eye cannot adapt to two whites at once, so one of the pair looks tinted and no amount of profiling fixes it. Proofing set-ups match the display's white to a D50 viewing booth for that reason.
A night-shift or adaptive-white feature is left on while colours are being chosen.
The screen's white has moved towards amber and every colour with it. Decisions made in that state look too cool on any other device.