Guide

Warm and cool: reading colour temperature

Temperature is what makes light feel like light. It is also relative, which is why it stays hard long after value has become easy.

Colour temperature is whether a colour leans warm or cool. Reds, oranges and yellows read warm; blues and blue-greens read cool. That much is easy. What makes temperature genuinely hard is that it is relative: a red can be the cool note in a passage full of hotter reds, and a blue can be the warm one beside a colder blue.

Getting temperature right is what makes light feel like light. Form turns because the light side and the shadow side differ in temperature as well as in value, and a painting where every shadow is just the local colour made darker looks like a diagram of an object rather than an object under a particular light.

Where warm and cool actually sit

Around the hue circle, the warm pole sits in the orange-reds and the cool pole in the blues, with two crossover regions where colours become ambiguous. This is roughly the scale BrushLens uses internally, expressed as a number from warmest to coolest:

The two crossover points are where painters lose their footing. Green sits almost exactly on the line and can be pushed either way by what surrounds it. Violet warms back up towards magenta, which surprises people who have learned "blue equals cool" as a rule.

Temperature is weaker in greys and at the extremes

Two things quietly reduce how much temperature a colour actually carries, and both matter at the easel:

• Low saturation. A near-grey has almost no temperature regardless of its hue. This is why temperature decisions in the muted passages of a painting are so delicate: there is very little signal there, and a small mixing error flips it.
• Very dark or very light values. A near-black or a near-white cannot carry much temperature either. A shadow that is genuinely almost black is closer to neutral than its hue suggests, and pushing it hard warm or cool will read as a mistake.

Shadows are usually cooler than you paint them

Under ordinary daylight, the light source is warm and the fill light is the blue of the sky. So lights go warm and shadows go cool, and the cool is stronger than most painters believe until they measure it. The common failure is a shadow mixed by adding black or brown to the local colour, which keeps the hue and kills the temperature shift, producing a shadow that looks like dirt.

The reverse case exists too. Indoors under a warm lamp with daylight coming through a window, the lights are warm and the shadows carry the window, or the lights are cool and the shadows pick up warm bounce from the floor and walls. Look, rather than applying the rule.

Toning the ground to match

Once you know which way the picture leans, tone the canvas to work with it rather than against it. A few starting points:

• Warm shadows: a thin wash of yellow ochre or transparent oxide red, so the warm undertone shows through in the darks.
• Cool shadows, warm lights: a thin ground of yellow ochre and white, then push cool notes into the shadows with ultramarine.
• Cool throughout: a neutral or slightly cool ground, mixed from ivory black and white to a mid value.
• Warm throughout: transparent oxide red or Van Dyke brown thinned down, and save your blues for the few cool accents you need.

Written by Soren Ulsig. Last updated 2026-08-29.