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. Put one warm note next to it — a creamy magnolia, a honeyed oak, brass hardware — and it curdles. It goes flat and slightly mauve. So the rule is simple: keep the whole envelope cool and quiet.
For woodwork, you want a soft cool white rather than a yellow-based one. Both Paper III from Paint & Paper Library (LRV 75.3) and Farrow & Ball's Au Lait (LRV 80) sit beautifully here — bright enough to lift the ceiling and trim without throwing warmth back at the blue. 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 feature colour. Don't add a warm accent. 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. Mylands Cigar BH.20 (LRV 11.8) is a properly moody near-black that grounds the scheme without warming it up.
If you genuinely want a pop of colour — and this is the one warm-ish exception that works because it's a true complementary — Dulux Fuchsia Falls 2 (LRV 29.8) sits opposite blue on the wheel and gives you a considered, slightly dusty pink accent on a cushion or a piece of art. 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.