If you want Pale Walnut but would rather buy from Dulux's standard range — usually cheaper and easier to get mixed at trade counters — Stone Sensation is your answer. It lands at ΔE 1.1 from Dulux Heritage Pale Walnut — a whisker over the strictly imperceptible line (that's anything under 1) and well inside "very close" territory. In practice, once it's dry on the wall you won't spot the difference. The lightness is as good as identical too — Stone Sensation reads at LRV 59.7 against Pale Walnut's 59.9 — and it shares that same balanced putty-greige character, warm brown softened with a whisper of grey.
The runner-up is Dulux Subtle Seashell at ΔE 1.6. Still very close, but it sits a few points lighter at LRV 63.5 and leans warmer, with a gentle pink-peach undertone where Pale Walnut stays calm and putty-neutral. In a dim room that touch of extra light can be welcome; if it's Pale Walnut's bleached-timber steadiness you fell for, Stone Sensation is the truer twin. Worth knowing: Dulux's Caramel Sand 5 is the same measured colour as Subtle Seashell under another name, so if your stockist's deck shows one and not the other, pick whichever they'll mix.
The "but what about" here: people assume the Heritage line is just standard Dulux with a posh label. It isn't — the Heritage range uses a different base and tends to have a denser, flatter finish with better depth, especially in the matt. So while Stone Sensation matches the colour almost perfectly, the Heritage Pale Walnut will look a hair richer in certain lights because of how the paint film behaves, not the pigment. For most jobs that's a non-issue.
Practical advice: order testers of both Stone Sensation and Subtle Seashell, brush two coats onto A3 boards, and prop them against the wall morning and evening before committing. Match figures get you 95% of the way there — your own light does the last 5%. Pale Walnut itself is remarkably steady as the light shifts — warm light nudges up the brown, cool light the grey — so a proper match should behave just as gracefully. If budget's the driver and you just want Pale Walnut on a wall, go Stone Sensation and don't look back.