The honest answer is that the best bathroom colour depends on the room — but there are clear winners, and they fall into three camps: calming blues, restful greens, and warming off-whites.
Bathrooms suit colour better than almost any room because they're small, you're in there briefly, and you can be bolder than you'd dare in a living space. Soft blues are the classic for a reason — they read clean and spa-like. Farrow & Ball Mizzle is a gorgeous grey-green-blue that shifts with the light and never feels cold. For something with a bit more depth on the walls of a larger bathroom, Inchyra Blue or Treron look superb against white sanitaryware and brass taps.
Greens are the other dependable choice. Little Greene Aquamarine and F&B Card Room Green both bring a relaxed, natural feel without going full jungle. They flatter chrome, brass and brushed nickel alike.
If your bathroom is small or north-facing, don't fight the lack of light with stark brilliant white — it'll just look grey and clinical. Reach for a warm off-white instead: F&B Pointing or Slipper Satin keep things bright but soft.
Now the bit that matters more than colour: the finish. Bathrooms are wet, humid rooms, so you want a paint that can cope. Most of the supported brands do a moisture-resistant emulsion — Dulux Easycare Bathroom, Crown's bathroom range, or Little Greene's Intelligent Eggshell for areas that get splashed. Earthborn Claypaint is breathable and brilliant for managing condensation if your extraction is decent.
What about the bit behind the basin and around the bath? Skip standard matt emulsion there — it'll grow mould. Use a wipeable mid-sheen or a proper eggshell on any zone that gets damp.
My practical advice: sample three colours on the wall furthest from the window, live with them for a couple of days through different light, and don't commit until you've seen them at night under your actual bathroom lighting. That's where most bathroom colour regrets happen.