Sheen matters more than the colour

A flat matt finish absorbs light and hides an imperfect wall, which is why it suits older houses and ceilings. It also marks easily and cannot be scrubbed, which is why it is wrong for a hallway with children in it.

Eggshell and satin reflect a little, wipe clean and show every ripple in the plaster beneath. On a wall that has been skimmed recently they look crisp; on a hundred-year-old wall they look like a bad plastering job, because they reveal one.

Test patches are routinely judged in the wrong conditions. Paint a large sheet of paper rather than the wall itself, then move it around the room across a full day: the north wall in the morning, the south wall in the afternoon, and under the lamps at night. A colour that works at all three is genuinely the right colour.

Ceilings are rarely the same white as the walls in a well-finished room. A ceiling in the wall colour at a much reduced strength, or a warmer white, avoids the hard line where two different whites meet, which is one of those details nobody notices and everybody feels.

Buy the better paint. The difference is opacity, which is the difference between two coats and four, and the labour saved exceeds the extra cost on the first wall.