Why does my room look wrong?

What it can diagnose

24 symptoms, with 31 distinct causes between them. Every cause carries the mechanism that produces the symptom, an honest statement of how well established that mechanism is, a test you can run today for nothing, and a set of fixes ordered from cheapest to most expensive.

The reason for the ordering is not modesty. The most common causes of a colour looking wrong in a room are the light it is seen under and what sits next to it — both of which are cheap to change — and the least common is that the colour itself was a bad choice. Advice that opens with “repaint it” gets the ordering exactly backwards.

Common questions

Why does it not just tell me what colour to paint the room?

Because repainting is the most expensive and least reversible thing you can do to a room, and it is frequently not the cause. A grey that looks green is more often a lighting or a contrast problem than a paint problem; a room that feels cold is more often short of warm materials or warm bulbs than short of warm walls. The tool works up from the cheapest intervention, and it only reaches repainting when the cheaper ones have been ruled out.

How does it decide which cause is most likely?

Each cause carries an evidence strength and a set of conditions. An established mechanism — simultaneous contrast, metamerism, the spectral behaviour of a warm bulb — starts higher than a design convention, because it is more likely to be what is actually happening. Then your answers move things: telling it you have cheap LEDs raises the rendering cause substantially; telling it you have an oak floor raises the contrast cause. Nothing is ever eliminated for lack of information, because not knowing your bulb's CRI is not evidence that the bulb is fine.

What is the difference between the evidence labels?

Three levels, and the distinction is real. 'Established' means a well-documented property of colour vision or of light — simultaneous contrast and metamerism are not matters of opinion. 'Widely observed' means the mechanism is plausible and the effect is real but its size varies by room. 'A design convention' means exactly that: a widely held view among decorators, worth knowing as a convention and not dressed up as physics. Roughly a third of what circulates as colour advice belongs in the third category and is presented as the first.

It says 'worth ruling out' — what does that mean?

That the cause is plausible but you have not told it enough to judge. It is a prompt rather than a verdict: each cause comes with a test you can do today for nothing, and doing that test is usually faster than answering more questions.

Can I use it if I am renting and cannot paint?

That is the case it is best at. Untick the wall colour under 'what are you willing to change' and every recommendation will work around it — which mostly means lighting, textiles and accessories, and those are where the cheapest fixes live anyway. If every remaining option depends on something you have ruled out, it says so plainly rather than pretending otherwise.

Does it know what my room looks like?

No. It knows what you told it, and it says which of its questions it is still unsure about. There is no photograph, no upload and nothing stored — everything is worked out in your browser. It also has no view on your room's proportions, what you own or what you like, and any of those can override what it says.