Often a smaller room with less natural light, where reflective tile and fixtures interact strongly with wall colour.

This bathroom is lit only by artificial light, with no visible window — exactly the condition where a colour that looked right in a well-lit shop can shift once painted, since there's no daylight to fall back on.
This is a wide panoramic room scene, not a single-material close-up — the palette was reviewed to represent the room's dominant wall, cabinetry and fixture tones under its own artificial lighting."Panoramic view of the first floor bathroom in a house along Tranquility Court in the Franklin Farm section of Oak Hill, Fairfax County, Virginia" by Famartin, CC BY-SA 4.0, via Wikimedia CommonsFixed materials: Tile and fittings are usually fixed and expensive to change — choose the wall colour to complement those rather than assuming a fresh coat can override them.
Directions that tend to work: Pale, reflective colours help a small bathroom feel larger; a bolder colour can work well below a tiled dado or on one wall only in a larger bathroom.
Colours that can be difficult: Cool, pale colours can look clinical or slightly green under some cool-white bathroom lighting — check under the room's actual bulbs.
Sage Green
green · medium
Powder Blue
blue · light
Duck Egg Blue
blue · light
Lavender
purple · pale
Sky Blue
blue · light
Mint Green
green · light
Terracotta
orange · medium
Mustard
yellow · light
Chocolate Brown
orange · deep
Burnt Orange
orange · medium
Camel
orange · medium
Ochre
yellow · medium
Coastal bathroom
Fresh, clean, quietly maritime.
Low-to-moderate contrast; the blue accent is the only saturated note in the room.
Bathrooms are frequently lit by artificial light alone — check the blue accent under your actual bulb colour temperature.
Black-fixture monochrome bathroom
Contemporary, graphic, confident in a small footprint.
High value contrast between pale walls and black fixtures is the entire point of this scheme.
Matte and gloss black fixtures reflect light very differently from each other — check the specific finish under the bathroom's actual lighting before committing.
See also: materials and interior goals.