How our compatibility engine works

Colour isn't a single number

A paint colour might look like one swatch on screen, but to our engine it's a small bundle of attributes: an undertone (the underlying warm, cool or neutral cast), a colour family, a tone (how light or dark it sits), and a sense of how clean or dirty the pigment is — whether it's a pure note or one muted with brown, grey or black.

Two colours rarely clash for one reason alone. They tend to feel "off" because several of these attributes are tugging in opposite directions at the same time. Our engine looks at all of them together, not in isolation.

A weighted conversation, not a checklist

Each pairing is run through a set of relationship checks, all weighted by how much the human eye actually cares about that relationship in a real room. Some of the things the engine pays attention to:

• How the two undertones sit on the colour wheel — gently complementary, quietly harmonious, or pulling against each other.
• Whether the tonal contrast is comfortable, flat, or visually jarring.
• Whether the cleanliness of the two colours is consistent enough that neither one makes the other look dull or muddy.
• How the colour family of each shade interacts with the other in traditional decorating relationships.

Each check produces a small contribution; the engine combines them into a single score. We then collapse that score into the simplest answer we can give you — a thumbs up if the pairing is comfortable to live with, a thumbs down if it isn't. We deliberately keep the answer binary on the listing page so it stays useful at a glance instead of asking you to weigh up percentages.

Why we don't show the maths

We've kept the precise weightings, thresholds and the order in which the checks are applied private. Two reasons. First, the recipe is the result of a lot of in-house testing and we'd rather not hand it to every other paint brand. Second, colour judgement is a craft, and the weightings change over time as we learn from real customers and real rooms — pinning them to a published formula would freeze something that's meant to keep improving.

How to use it well

• Star the colour you're most certain about. Usually that's the wall colour, or a piece of furniture you're keeping. The engine then tells you which of our other 99 shades will partner with it.
• Don't treat a thumbs down as a ban. A clash is just a warning that the pairing is harder to make work — it can still succeed in the right light, on the right wall, in the right quantity.
• Order matters less than feel. A thumbs up on screen still deserves a sample on your wall before you commit.