How to Extract and Use Colour Palettes from Reference Photos

One of the most underrated skills in painting and illustration is the ability to look at a reference photo and immediately identify its key colours — not the hundreds of individual hues that are technically present, but the five or six dominant colours that define the image's overall feel. Extract those, and you have a palette you can use directly in your work.

Why Dominant Colours Matter

A photograph contains thousands of distinct colour values. But our visual system doesn't process images as a cloud of individual pixels — it groups them into regions of similar colour and perceives those regions as shapes. When you look at a landscape photo, you might see a sky region, a midground region, and a foreground region, each with a dominant colour temperature and value.

Working from dominant colours rather than every colour has real practical benefits:

• Colour harmony. A palette of 4–6 dominant colours extracted from a single photograph is inherently harmonious, because they all exist together in a real scene under the same light source.
• Value structure clarity. When you simplify a reference to its dominant colours, the underlying value structure (dark vs. light areas) becomes much easier to see and plan around.
• Mixing efficiency. If you're painting in oils or acrylics, knowing your key 4–5 colours means you set up only those on your palette and mix from them — rather than reaching for 20 different tubes.
• Digital consistency. In digital illustration, working from a limited extracted palette keeps your colours consistent across a piece rather than letting colour drift with each new brush stroke.

How to Read the Colour in a Reference

Before reaching for a tool, train your eye to do this manually. When you look at a reference photo, ask yourself these questions:

1. What is the single largest colour area? Often the sky, a background wall, or a large fabric. This dominant colour will set the mood of the entire piece.
2. What is the overall temperature? Is the image warm (yellows, oranges, reds dominate) or cool (blues, greys, blue-greens)? This tells you about the light source and time of day.
3. Where are the darkest darks? What colour are the shadows? Shadows are rarely pure black — they're usually a deep, cool version of a nearby colour.
4. Where are the lightest lights? What colour are the highlights? In sunlight, highlights are often warm yellow-white. In overcast light, they're cool blue-grey.
5. What colour is the most visually surprising? Usually an accent — a small area of high saturation that draws the eye. This is often the smallest colour in your palette but one of the most important.

How the Colour Extraction Algorithm Works

SketchKit uses Median Cut quantization — a colour science algorithm developed by Paul Heckbert in 1982 — to find dominant colours. Here's the basic idea:

All the pixels in your image are treated as points in a 3D colour space (Red, Green, Blue). The algorithm then repeatedly splits the largest group of points along whichever axis has the widest spread, until it reaches the number of groups you requested. The average colour of each group becomes a palette entry, and the groups are sorted by size — so the largest group (covering the most pixels) appears first.

This means that if you extract a 5-colour palette, you're getting the 5 colours that, together, best represent the largest portions of your image by area. That's exactly what you want when analysing a reference for painting.

Applying the Palette to Your Own Work

Extracting the palette is only half the job. Here's how to actually use it:

In oil or acrylic painting

Set up only the dominant palette colours on your palette. Mix every colour you need from these — don't reach for tubes that aren't in the palette. This constraint creates colour unity across the painting. The extracted hex values give you a clear target to match when mixing.

In digital illustration

Import the palette by copying the hex codes directly into your colour swatches in Procreate, Photoshop, or Illustrator. You can also download the palette as a Photoshop .aco swatch file from SketchKit and load it directly into Photoshop's Swatches panel — no manual entry required.

In watercolour

Identify which 3–4 of your existing tube colours most closely match the extracted dominant colours. Pre-mix washes from these and use them to establish the underlying value structure before adding detail.

Understanding Colour Relationships in the Palette

Once you have a palette, look for these relationships:

• Complementary pairs. Are any two palette colours roughly opposite on the colour wheel? If so, they'll create visual vibration when placed adjacent. Use this intentionally for areas you want to draw attention to.
• Temperature shifts. If your dominant colours are warm but one is noticeably cool, that cool colour is probably in the shadows. This is often how natural light works — warm light, cool shadows — and recognising it will make your colour choices feel more natural.
• Value range. Convert the palette to grayscale mentally (or use SketchKit's Simplifier to do it physically). Do you have a full range from dark to light? If everything is mid-value, the reference may be overexposed or the painting will feel flat.

Practical Exercise: Palette Analysis

Pick a painting you admire — from any period, any style. Find a high-resolution image of it online. Run it through the colour palette extractor and request 6 colours. Now look at those 6 colours in isolation, without the painting context. Notice:

• What temperature dominates?
• What is the value range (lightest to darkest)?
• Is there a single accent colour that stands out from the rest?
• How many of the colours are neutrals (greys, browns, muted earth tones) vs. saturated hues?

Repeat this exercise with several paintings and you'll begin to see patterns — how limited the actual colour ranges of most paintings are, and how much of the perceived richness comes from the relationships between those few colours rather than the variety of colours themselves.

Building Your Own Reference Palette Library

Over time, build a personal library of extracted palettes from references you love — landscapes, interiors, figure paintings, photographs. Keep the palette images alongside notes about what worked and why. When starting a new piece, browse your library for a palette whose mood matches what you're going for, and use it as your starting point. This is how professional illustrators and concept artists work: they're not inventing colour combinations from scratch — they're drawing on a curated library of proven combinations they've analysed over years.