If you're after the Dulux equivalent of Borrowed Light, go with Celestial Cloud 6. It lands at ΔE 1.2 from the original (LRV 70.9), and anything under 1 is imperceptible to the eye — 1.2 means you'd need the two chips side by side in lab lighting to spot a whisker of difference. On a wall, nobody's clocking it.
Your second option is Steel Symphony 6 at ΔE 1.5 (LRV 71.2). Still a very close match, just a touch further off. Both sit in that pale, airy blue-grey territory that makes Borrowed Light such a darling for bedrooms and bathrooms — soft, a bit chalky, never icy.
Here's the thing though. Borrowed Light is a colour that *lives* on its undertone. It can read almost white in a north-facing room under flat grey light, then bloom into proper powder blue when the sun hits. That shifting quality is half the reason people love it. A Dulux match nails the hue at the chip level, but you won't get F&B's pigment depth or that slightly matte, light-eating finish from the same can. The colour's right; the *character* is subtly different.
So if you're matching to existing F&B walls — touching up, or doing a connecting room — Celestial Cloud 6 will blend beautifully. If you're starting fresh and just want the look for less, it's a cracking shout too.
One practical note: paint a decent-sized board (A3 minimum), prop it against the wall, and watch it across a full day before you commit. Borrowed Light and its matches all swing hard with the light, and a tester pot is cheaper than a regret. Order both Dulux samples if you're undecided — at 0.3 ΔE apart, the deciding factor will be your specific light, not the spec sheet.