There's no perfect Dulux twin for Squid Ink, but the nearest you'll get is Dulux Smokey Slate (LRV 12.3) at a ΔE of 3.6. That's a noticeable-but-acceptable difference — close enough that most people wouldn't clock it on a wall, though a paint matcher with the two chips side by side would. The runner-up is Dulux Winters Sky (LRV 9.8) at ΔE 4.2, which reads a touch deeper and slightly cooler.
For context: a ΔE under 1 is imperceptible and under 2.5 is what I'd call a very close match. At 3.6, Smokey Slate isn't in that bracket — it's a *good* match, not a dead ringer. So manage your expectations, mate. If you're touching up an existing Squid Ink wall, don't bank on either Dulux colour blending invisibly into the old coat. For touch-ups, always go back to the original Paint & Paper Library tin if you can.
Where these Dulux alternatives earn their keep is on a fresh job — a new room, or a whole repaint — where you want that moody, inky blue-grey character but prefer Dulux's availability and price point. Both Smokey Slate and Winters Sky deliver that smoky, slightly green-leaning depth that makes Squid Ink so good in north-facing rooms and hallways.
One thing to watch: deep colours like these eat light, and the small LRV gap between them (12.3 vs 9.8) means Winters Sky will feel a shade closer to true dark. In a gloomy room, Smokey Slate gives you a hair more bounce.
My advice — order sample pots of both Dulux options and a Squid Ink sample, paint big patches, and live with them across a full day. Colour matching by numbers gets you to the shortlist; your own eye in your own light settles it. Brush the patches on lining paper so you can move them between walls before committing.