Mixing guide
How to mix the color of a sky
A sky is not one blue. It is a gradient that goes lighter, warmer and duller towards the horizon.
Painted skies go wrong when they are painted as a single blue. A clear sky is darkest and most saturated directly overhead and gets lighter, warmer and greyer as it comes down to the horizon, because you are looking through progressively more atmosphere.
That gives you at least three mixtures for what looks like one area. The zenith wants a strong blue with very little white; the middle wants more white; the horizon wants white with a trace of blue and often a touch of something warm.
Which blue matters too. Ultramarine leans violet and works well overhead; cerulean is cooler, grainier and weaker, which is exactly what you want near the horizon.
The mixtures
Each one worked out on a real palette with the spectral model. The number after the mixture is how far it lands from the target: under 2 you cannot see the difference, under 4 it does not matter in a painting.
Zenith blue #4A7EC0
Straight overhead on a clear day. The most saturated part of the sky.
5× Ultramarine +3× Titanium White +1× Phthalo Blue
5× Ultramarine +1× Phthalo Blue
Thin wash, roughly 1 part paint to 4 parts water.
5× Ultramarine +3× Titanium White +1× Phthalo Blue
Mid sky #8FB4DA
Halfway down. Lighter, slightly less blue.
9× Titanium White +2× Ultramarine +1× Phthalo Blue
5× Ultramarine +3× Viridian
Very thin wash, roughly 1 part paint to 19 parts water.
9× Titanium White +2× Ultramarine +1× Phthalo Blue
Horizon haze #C8D3DC
Warm, pale and almost neutral.
10× Titanium White +1× Ultramarine
5× Payne’s Gray +2× Ultramarine
Very thin wash, roughly 1 part paint to 49 parts water.
10× Titanium White +1× Ultramarine
Cloud shadow #9098A3
The underside of a cumulus. Cooler and darker than people expect.
10× Titanium White +3× Ultramarine
8× Ultramarine +7× Burnt Sienna +2× Phthalo Blue
Very thin wash, roughly 1 part paint to 12 parts water.
6× Titanium White +5× Ultramarine +1× Lemon Yellow
This palette cannot quite reach that color with 3 pigments in one mixture. What you see is the closest it gets, which is worth knowing before you spend an afternoon trying.
Worth remembering
- Mix all your sky values before you start, and lay them wet into wet so the transitions stay soft.
- A sky is usually lighter than a beginner paints it and darker than a photograph suggests.
- Clouds are rarely white. The lit side of a cloud is warm; the underside is a cool gray that often sits darker than the sky behind it.
Your paints, your photo
These mixtures assume the palettes above. Tick off what you actually own and pick the color straight out of your reference instead.