Edward Bulmer makes lovely paint — proper natural pigments, plant-based, genuinely breathable. But it's premium-priced, and if it's purely the *colour* of Ethereal Blue you're after, you've got two cracking alternatives that come in cheaper.
The best match is COAT Hamilton at ΔE 2.4 from the original. Anything under 2.5 is what we'd call very close — you'd struggle to tell them apart on a wall. Don't let the name throw you, either: Hamilton is a soft sage-green on COAT's card, and it sits this close because Ethereal Blue is itself a muted, green-leaning blue — the two meet in the same calm grey-green territory. Hamilton sits at LRV 48.1, so it bounces a fair bit of light around and feels calm rather than cold. COAT is water-based, low-VOC, and sells direct so the pricing is sharp.
Close behind is Dulux Highland Falls 3 at ΔE 2.6, with an LRV of 45.5 — just past the very-close line, so a careful eye would pick it out side by side. It's a hair more muted than the original and a touch lighter with it, and Dulux availability means you can grab a tester from any decorator's merchant tomorrow. For the money, it's a sensible shout.
I'd steer you away from Crown Curiosity here — at ΔE 5.4 and LRV 37.2 it's noticeably darker and reads as a different, deeper colour entirely. Not a match, even if it's in the same family.
Now, the honest caveat: a ΔE match gets you the colour, not the finish. Edward Bulmer's pigments give a particular chalky, light-absorbing depth that the cheaper acrylics won't replicate exactly, especially in low north-facing light. If Ethereal Blue is going on a feature wall you'll live with closely, order testers of both Hamilton and Highland Falls 3 and paint them up big — A4 minimum, two coats, viewed morning and evening.
If breathability and natural ingredients were the *reason* you wanted Edward Bulmer in the first place, don't swap — you'd be losing the point. But if it's just the colour you love, Hamilton gets you there for less.