Test a sample for 48 hours before painting

A colour never exists in the abstract. It depends on the light that hits it, the surface it is applied to, the neighbouring colours, and the time of day. The same Farrow & Ball white appears cream in a south-facing room, grey in a north-facing one, yellow under a warm bulb, blue under a cold LED.

That is why the swatch in the shop, the open tin on the workbench, and the finished wall in your home are three different colours. Not slightly different. Genuinely different. The only way to know is to paint a large sample directly on the actual wall and observe it over two full days.

Forty-eight hours is the minimum to see the colour under the three main lighting conditions: morning, midday, evening. And under two weather states: clear sky, overcast sky.

The method comes down to five simple steps.

1. Buy a tester pot (approximately 100 ml) from your supplier. Major brands like Farrow & Ball, Little Greene and Fired Earth offer them. Avoid paper swatches, their rendering is off by 50%.

2. Paint a square of at least 50 cm on the actual wall you intend to paint. Not on a sheet of cardboard, not on the adjacent wall. The light hitting your sample must be exactly the light that will hit the finished wall. If you are testing several shades, space the samples at least 30 cm apart to avoid visual contamination.

3. Observe at three moments: morning (8–10am), midday (12–2pm), evening (5–7pm). If possible, also in artificial light after 8pm. Note your impressions each time, yesterday's memory is unreliable.

4. Live with it. Walk around it, put a piece of furniture in front, hold a cushion in the colour of your sofa next to it. Colour does not exist alone, it exists with the other elements of the room.

5. Decide only after 48 hours. If after two full days you are still hesitating, it is not the right one. The right colour asserts itself.

At Farrow & Ball, interior designers recommend a 1 m² sample for rooms over 30 m². The eye needs proportionate scale to anticipate how a colour reads across a large surface.

Pierre Yovanovitch keeps his samples on the wall throughout the design phase, sometimes for several weeks. He says good colours confirm themselves with time, bad ones reveal themselves after a few days.

Another practice, less common, is to paint two entire walls for undecided clients before signing off, and to live with them for a week. The cost is negligible compared to the price of a failed room that will need repainting.