How to test a colour

Cool tubes overhead, a neutral counter, a white card, a mirror angled to flatter. Retail lighting is engineered so that nothing looks bad, which makes it useless as evidence. A colour can only be judged where it will be worn or lived with, at several hours of the day, over a period that will feel excessive to anyone in a hurry.

Paint shops and beauty halls share a lighting philosophy. The tubes run cool and bright, the surfaces are neutral, the sample is presented against white. White is the most aggressive backdrop available: it pushes every pigment towards its own opposite, so warm colours read warmer and cool ones colder purely by contrast. A foundation swatched on the back of a hand is being assessed against skin that is not the skin it will sit on, in light that exists in almost no domestic room in Britain. The variable formulators worry about, and that shoppers are rarely told about, is metamerism. Two colours can match precisely under one light source and separate under another, because the pigments producing them reflect different parts of the spectrum while arriving at the same coordinates for that particular illuminant. It explains the foundation that vanished at the counter and turns faintly grey in a bathroom, and the soft warm grey from the chart that goes violet at four in the afternoon. Nothing in the product has changed. The light has changed, and the light was always doing most of the work. Daylight is not one thing either. Colour temperature across a single London day travels a long way, from something near neutral at midday to a distinctly blue cast under heavy cloud, and the light entering a room carries the colour of whatever it struck first: brick, wet pavement, the green of a plane tree in leaf. A north-facing room receives almost nothing but that reflected light, which is why northern rooms are unkind to anything with yellow in it, and why the same room flatters some complexions and drains others.

Testing properly means surrendering the pleasure of deciding quickly. The method holds whether the surface is a wall or a jawline: put the colour where it will be seen, leave it there, and return to it at hours that are inconvenient, including after dark.

For paint, the sample needs to be large and it needs to be movable. Two coats on a sheet of lining paper, at least A2, left to dry fully rather than judged wet, gives something that can be propped against each wall in turn and carried to the darkest corner. Painting a patch directly onto an existing colour is close to worthless, since the surrounding shade will distort it in both directions. The sheet should be looked at early in the morning, at the middle of the day, at dusk when the room turns, and under the lamps that will actually light it in winter. For foundation, the equivalent discipline is a stripe along the jaw and lower cheek, never the wrist, and then a full day of ordinary life. Most formulas shift over the first three to four hours as they oxidise and settle into sebum, so the shade that matched at nine can be a full step darker by lunch. The relevant checks are a window, an unflattering bathroom mirror, and a photograph taken by someone else, which is the only view of the face that matches how other people see it. What this costs is time, and the willingness to live with an undecided wall or an unfinished face for a week. What it saves is the more expensive error: four walls in a colour that only ever worked on the chart, or a drawer of bottles bought under tubes and abandoned in daylight. The principle is unglamorous and transfers cleanly between the two industries. Judge the colour in the conditions of use, repeatedly, and give it long enough to misbehave.