Willow Tree is a soft, slightly yellowed sage — the kind of green that turns muddy the second you put a stark brilliant white next to it. So the first rule is simple: skip the bright white trim entirely.
Ground it instead with a warm off-white on your woodwork and ceiling. Farrow & Ball Au Lait (LRV 80) is spot on — creamy enough to flatter the green without throwing it cool. If you want something a touch lighter and chalkier, Paper III from Paint & Paper Library (LRV 75.3) does the same job and keeps the whole scheme breathing. Either of these reads as "white" in the room while quietly supporting the green rather than fighting it.
For depth and contrast, go to the umber and olive end of things. Mylands Cigar BH.20 (LRV 11.8) is a gorgeous deep tobacco-brown that works beautifully as a feature — a fireplace surround, a piece of joinery, or pulled through in textiles. It echoes the warmth already sitting inside Willow Tree, so the room feels collected rather than busy.
Want a proper accent with some life in it? Dulux Fuchsia Falls 2 (LRV 29.8) gives you a dusky pink-purple that sits opposite the green on the wheel — brilliant for cushions, a chair, or a single bold door. Use it sparingly; one hit is enough.
Now the bit people get wrong: hardware and metals. Cool chrome and polished nickel will kill this scheme stone dead. Go for unlacquered brass on knobs, taps and light fittings — it ages into the warmth perfectly. Terracotta floors or earthy clay tiles do the same job underfoot, pulling the yellow forward.
Practical advice: paint a large board with Willow Tree, prop your Au Lait or Paper III sample against it, and check it morning and evening before committing. Greens like this shift more than most across the day, and a north-facing room will pull it greyer than a south-facing one.