Messel No.39 is one of those Mylands colours that rewards commitment. Don't half-paint it with a crisp white above the picture rail — it'll look municipal, like a council corridor. Drench it. Walls and woodwork in the same colour, top to bottom, and let it wrap the room.
The trick to keeping a deep shade like this from feeling oppressive is layering warmth, not contrast. Take the ceiling — and any adjacent lighter surfaces — into a soft warm off-white rather than a brilliant one. Paper & Paper Library Paper III (LRV 75.3) or Farrow & Ball Au Lait (LRV 80) are both ideal here. They're creamy enough to glow against the depth of the Messel without that jarring blue-white shock you'd get from a cool white. Au Lait in particular has the soft, milky quality that flatters dark rooms beautifully.
For accents, go richer and warmer still. Mylands Cigar BH.20 (LRV 11.8) is a gorgeous tobacco-brown that picks up the earthy undertones — perfect on a piece of joinery, an interior door, or a built-in. For something with a bit more drama, Dulux Fuchsia Falls 2 (LRV 29.8) brings an oxblood-leaning richness that sings against Messel; think cushions, an armchair, or a single bold wall in a connected space.
Metals matter enormously with a colour this saturated. Keep everything warm — aged brass, antique bronze, unlacquered copper. Chrome and bright nickel will look cold and out of place; they fight the whole scheme.
Practically: test it big, and live with it across a full day. Deep colours shift dramatically between morning and lamplight, and Messel will look very different under a warm bulb than it does in daylight. If you're nervous about going full-drench, start with the ceiling in Au Lait and the walls in Messel — that alone will tell you whether you've got the appetite for the woodwork too. You usually have.