Right, let's kill the myth first: there's no law saying ceilings must be brilliant white. That habit comes from builders' finish, not good design. A stark white ceiling over a coloured wall creates a hard line where the two meet, and it can feel like a lid clamped on the room.
Here's how I'd think about it.
Lighter, neutral rooms — go ahead and bring the ceiling down a notch from pure white. Brilliant white is genuinely cold and a bit harsh. Reach for something soft instead: Farrow & Ball Wevet or Pointing, or Little Greene Loft White. These read as white to the eye but lose that clinical edge, and they sit far more comfortably above a warm wall colour.
Cosy or small rooms — paint the ceiling the same colour as the walls. Sounds bold, looks brilliant. Wrapping a deep colour like Farrow & Ball Inchyra Blue or Hague Blue over the ceiling makes the boundaries dissolve and the whole room feel like a snug, enveloping box. Snugs, studies and bedrooms love this. Drop the sheen — a flat matt or estate emulsion finish on the ceiling avoids glare and hides imperfections.
A neat middle path — take your wall colour and have it knocked back to 25–50% strength for the ceiling. Most of the supported brands will mix this, and it keeps everything in the same family without the contrast jarring. F&B's own ceiling-white-tinting trick works the same way.
The one place to keep things light and bright is a north-facing room with low ceilings — there a soft off-white ceiling lifts the available light rather than soaking it up.
Practical bit: always use a dedicated matt ceiling emulsion or a flat finish — never eggshell or anything with a sheen up top, because raking light from windows will show every roller mark and plaster flaw. And cut in carefully where wall meets ceiling; a tinted ceiling is far more forgiving of a slightly wobbly line than stark white ever is.