Ethereal Blue is exactly what the name says — a delicate, airy, slightly washed-out blue. The thing to understand about a colour like this is that it lives and dies by the temperature of everything around it. Load the room with rich, honeyed warmth — magnolia creams, orange-toned timber, gold light — and it curdles, going flat and slightly mauve. So the rule is simple: keep the envelope soft and quiet, and make any warm note a deliberate one rather than an accident.
For woodwork, you want a soft, quiet white rather than a stark brilliant one. Both Paper III from Paint & Paper Library (LRV 75.3) and Farrow & Ball's Au Lait (LRV 80) sit beautifully here — gently warm, milky off-whites that lift the ceiling and trim without the harsh blue edge of a brilliant white. A soft off-white against a pale blue reads as deliberate, easy contrast; what you're avoiding is a rich cream, which drags the blue mauve. Au Lait in particular has a clean, milky quality that flatters Ethereal Blue rather than fighting it.
Where people go wrong is reaching for a loud feature colour. Add depth instead. A deeper slate-blue or grey-green gives you contrast within the same cool family — think a chimney breast or a single dark joinery run that anchors all that lightness. Or make the warm note the deliberate one: Mylands Cigar BH.20 (LRV 11.8) is a smoky mid-depth tobacco brown, and used on one considered piece — a door, a bookcase — it grounds all that airy blue like branch against sky.
If you genuinely want a pop of colour, Dulux Fuchsia Falls 2 (LRV 29.8) is a bright, cool magenta-pink — it shares the blue's cool temperature, so it reads as a clean jolt of contrast on a cushion or a piece of art rather than a warm intruder. Use it sparingly. It's a punctuation mark, not a wall.
For the hard finishes: pale washed oak floors and polished nickel taps and handles. Nickel reads cool and silvery where brass reads warm and gold — and that distinction matters enormously with a colour this sensitive.
Practical tip: paint a board and view it on a north wall at dusk. If it ever looks lilac, something warm has crept in — usually the lighting or a nearby timber tone.