What really enlarges a room
Three things, and colour is only the first. Brightness: the more light a colour returns — which is what the LRV shown on each colour measures — the further away the walls seem. Above 60 you enlarge; below 30 you envelop. Continuity: a white line at the ceiling, a white rectangle around each door, a skirting that cuts — each of those outlines tells the eye where the room stops. Paint the ceiling and woodwork in the wall colour, or a barely different shade, and the room has no more limits. Temperature: pale blues and greens recede — they are the colours of distance — while warm whites brighten a dark room. A small south-facing room can take Morning Blue No.32 or Glass BH.09; a small north-facing one will prefer Sleet No.91, Copper Green No.36 or Kensington Rose No.22.
The pure-white trap
Pure White No.1 returns more light than any other colour — when there is some. In a dark room it has nothing to return: it turns grey in the corners, and those grey corners draw the room more sharply than a soft white would. That is why Sleet No.91 often enlarges more than a pure white.
The finish
Matt, always: Marble Matt Emulsion diffuses light in every direction and blurs the corners, where a sheen underlines them with its reflections. To paint the woodwork in the same shade as the walls, Multi-Surface Dead Matt.
To go further: our 8 colours for colour drenching, our warm whites for a dark room and our colours for a dark hallway.