If you want Stone II out of a Dulux tin, Gooseberry Fool 6 is your answer. We've measured it at a ΔE of just 0.5 from the original — that's well inside the threshold where the human eye stops noticing any difference. With an LRV of 81.4 it sits in that lovely soft, light-but-not-stark band, which is exactly what people love about Stone II in the first place: a warm off-white with a creamy backbone rather than a cold grey.
If for whatever reason your local stockist hasn't got Gooseberry Fool mixed up, Vanilla Mist 4 is your fallback. It comes in at ΔE 1.2 with a slightly higher LRV of 85.4, so it'll read marginally lighter and a touch brighter on the wall. Still a very close match — under 2.5 ΔE is what we'd call very close — but Gooseberry Fool is the one to go for if you can.
Now, the honest caveat. A tight ΔE on paper doesn't always translate one-for-one on the wall, because Paint & Paper Library and Dulux use different bases and finishes. PPL's pigment load and the way their matt emulsion handles light is part of why their colours feel the way they do. The Dulux match will get you the colour bang on, but the depth and chalkiness of the finish can differ slightly. For most rooms nobody will ever clock it.
My advice: buy a tester of Gooseberry Fool 6, paint a decent A4-sized patch — two coats — and live with it for a couple of days before you commit to the whole room. Check it in morning and evening light, and against any existing Stone II you're matching to. If you're trying to match a wall that's already in Stone II rather than start fresh, get both up side by side before you paint the lot. That's the only way to be properly sure.