Mallard Green is a deep, confident teal-green, and the trap is treating it like a neutral. It isn't — it's a jewel tone, and it performs best when you lean into that.
Start with your softening colour, because a dark green this saturated needs breathing room on ceilings, trim or the fourth wall. Farrow & Ball Au Lait (LRV 80) is a creamy, gently warmed white that stops Mallard reading cold — it's far kinder here than a brilliant white, which would look stark and clinical against all that depth. Paper III from Paint & Paper Library (LRV 75.3) does a similar job with a touch more grey, ideal if you want the room calmer rather than cosy.
Then the drama. Mallard absolutely loves a deep pink or fuchsia as an accent — think velvet cushions, an armchair, a single piece of joinery. Dulux Fuchsia Falls 2 (LRV 29.8) is the move if you're feeling bold; the contrast is rich and properly grown-up, not garish.
For a more masculine, library-ish scheme, bring in Mylands Cigar BH.20 (LRV 11.8), a deep tobacco brown. Two dark tones together — green and brown — read as luxurious and enveloping, the classic study or snug palette. Add brass hardware, a polished timber floor and you've got a genuine jewel-box.
The "but what about" question: can you do Mallard with grey? You can, but it tends to flatten the room and waste the colour's warmth. Mallard is at its best with warm companions — creams, ochres, pinks, tobaccos — not cool greys.
Practically: paint Mallard on the walls, Au Lait on the ceiling and trim, then layer the deep accents through soft furnishings rather than more paint. That keeps it sophisticated rather than overwhelming. And always test in your actual light — a deep green like this shifts noticeably between a north-facing room and afternoon sun.