Cornforth White is one of Farrow & Ball's most-loved soft greys — a warm, putty-leaning neutral that goes a touch pinky in north light and properly grey in cool, even light. The good news is you don't need to pay F&B money to get it on your walls.
The standout match is Dulux Pale Taupe (LRV 61.4), which lands at ΔE 0.7 from the original. That's well under 1 — meaning the difference is imperceptible to the human eye. Side by side on a wall you'd struggle to tell them apart, and Dulux's Diamond Matt is tougher and more wipeable than F&B's Estate Emulsion, which is a real plus in hallways and family rooms.
If you want something with a bit more clay warmth, Crown Clay Like (LRV 63.5) comes in at ΔE 1.4 — very close, and a smidge lighter, which can help in a darker room. COAT Margot (LRV 58.4) sits at ΔE 1.6, also very close, and COAT's matt emulsion is genuinely excellent paint with low odour and proper coverage. Margot reads slightly deeper, so it'll hold its grey a little better in bright rooms where Cornforth can wash out.
The "but what about" here: people worry the cheaper match won't behave the same in changing light. Honestly, at these ΔE figures the colour is essentially identical — what differs is the finish, sheen and how the pigment is bound. F&B's chalky depth is part of what you pay for, and Margot from COAT gets closest to that flat, characterful look.
Practical advice: don't buy on a swatch alone. Get a peel-and-stick sample or a tester pot, paint two coats on a bit of lining paper, and move it around the room across the day. North-facing? Expect any of these to lean cooler and slightly mauve. South-facing? They'll warm up nicely. Pick based on how it sits at the time of day you use the room most.