Ammonite is one of F&B's most useful warm-leaning greys, but it has a subtle violet undertone you need to respect. Get that right and it's a quietly sophisticated colour; get it wrong and it turns cold and a bit mauve.
Use it as an envelope. Ammonite genuinely shines when you run it across walls and woodwork together — same colour, different finishes — for a seamless, tonal room. It's calmer and more grown-up than chopping the trim out in white. If you must break it up, go for a cool-toned off-white on the ceiling rather than brilliant white. A stark white will throw Ammonite's violet note into sharp relief and make it look chilly.
For accents, the rule is muted, not saturated. Anything bright fights it. A soft, faded sage like Dulux Almost Pistachio (LRV 80.3) is a lovely partner on a connecting hallway or a quiet adjoining room — light, gentle, and it warms Ammonite up nicely. For contrast and depth, reach for muted mid-to-deep tones rather than primaries.
If you want drama, Paint & Paper Library Blue Blood (LRV 16.4) is a cracking faded inky blue — use it on a study door, joinery or a feature panel and Ammonite reads beautifully as the lighter neutral around it. And Mylands Cigar BH.20 (LRV 11.8), a rich tobacco brown, gives you warmth and grounding without anything garish — gorgeous on a cabinet, dado or fireplace surround.
The "but what about" question is usually flooring and light. North-facing rooms can push Ammonite cooler and emphasise that violet, so always test a big board against the wall before you commit — Ammonite shifts more than most greys depending on light. South light is far more forgiving.
Practical advice: paint two coats on lining paper, move it round the room over a full day, and check it against your floor and curtains, not just the wall. If it's pulling mauve, warm the scheme up with the Cigar or the sage rather than fighting it with white.