White balance: why photos come out yellow or blue

White balance is a camera setting that compensates for the colour of the light so that white objects in a photo look white rather than yellow, blue or greenish. It is measured in kelvin (K): warm light is about 2700-3000K, daylight 5500-6500K.

White balance makes white look white

In plain words

Your brain automatically "knows" a sheet of paper is white - under a warm lamp and in the shade alike. A camera cannot do that: to it, paper under a lamp is yellow. White balance is the camera trying to "think like a brain" and say: "This sheet should be white, so I will remove the extra yellow from the whole frame."

How it works

The camera analyses the scene and looks for neutral (grey or white) areas.
It estimates the colour temperature of the light.
Processing shifts the colours of the whole frame so the neutral areas become neutral.
AI recognises scenes (sunset, indoors, snow) and corrects them differently.
In Pro mode you can set white balance manually in kelvin.

Colour temperature of different light sources

Where you'll see it

In phone cameras it is automatic; in Pro mode it is a separate WB or K setting. Photo editors have it too (the "Temperature" and "Tint" sliders). Some phones have dedicated colour sensors for more accurate white balance.

Does it matter when buying

White balance decides whether faces look natural. Different phones have different "tastes" - some warmer, some cooler. If a photo under a lamp comes out yellow, fix the temperature in an editor; with RAW you can do it without any loss.

Myths

Myth: White balance is about brightness. Reality: It is about colour, not lightness.
Myth: Auto white balance is always right. Reality: In mixed light (lamp plus window) it often gets it wrong.

FAQ

What is colour temperature?

A measure of the tint of light: lower is warmer (yellow), higher is cooler (blue).

How do I fix a yellow photo?

In an editor, lower the "Temperature" slider or use the eyedropper on a white object.

What are "warm" and "cool" tones?

Warm has a yellow tint; cool has a blue one.