Adulting is a mid grey-green — a muted, slate-sage sort of colour with a soft blue-grey undertone that comes forward in cool light (LRV 16.2). People often clock it as a blue at dusk; on the wall it settles as a proper grown-up green-grey. The cleverest move is to drench the room: walls and woodwork in the same colour for the most resolved, enveloping result. That's how this colour looks best, full stop.
If you want a ceiling break, go soft but never stark. Farrow & Ball Au Lait (LRV 80) is a lovely milky white that takes the chill off without going yellow, and Paper III from Paint & Paper Library (LRV 75.3) does the same job with a quieter, stonier cast. Both keep the room calm rather than clinical — a brilliant white overhead would fight the muted green and make it look harsh.
For contrast and grounding, Mylands Cigar BH.20 (LRV 11.8) is your hero. It's a smoky tobacco brown sitting just a shade deeper than Adulting — think skirting, a feature joinery run, or a piece of furniture. Green-grey against brown reads expensive and very grown-up.
Want a bit of life? A measured hit of Dulux Fuchsia Falls 2 (LRV 29.8) — a bright, cool magenta-pink — brings personality: a single panel, the inside of a cupboard, or soft furnishings. Used sparingly it stops the scheme going sombre.
Metals and timber: blackened steel and aged bronze suit the colour's cool, muted register, and pale oak keeps things fresh rather than heavy. Bright yellow brass is the riskiest choice here — if you use it, make it one deliberate, aged piece rather than a scatter of shiny fittings.
My practical advice: drench first, then add Au Lait or Paper III above if the room feels low, ground with Cigar, and keep the fuchsia as a whisper. Sample big — two coats on a board you can move — and look morning and evening: in north light the blue-grey side comes forward, in lamplight the sage warms through.