Livid is one of Little Greene's brooding blue-greys — moody, smoky, with real depth. The nearest Dulux match is Midnight Garden at ΔE 2.9. That's in the "close enough for most rooms" bracket but, I'll be straight with you, it's not imperceptible. A ΔE under 1 is a true match; under 2.5 is very close; 2.9 means a sharp eye in good light will spot a slight shift. Midnight Garden sits at LRV 21, so it reflects a similar amount of light and will behave much the same way Livid does on a wall.
The runner-up is Neptune Seas at ΔE 3.5, LRV 17.1. That's a noticeably deeper, darker reading — the lower LRV tells you it'll swallow more light and feel more enclosing. If you're matching into an existing scheme of Livid, go Midnight Garden. If you're starting fresh and fancy something a shade moodier, Neptune Seas is worth a look in its own right.
Here's the honest bit, though: neither is a dead-on match, and Livid has a particular complexity that comes partly from Little Greene's pigment-rich formulation. Dulux matches the colour but not the depth of finish. If the actual Little Greene colour matters to you — and on a feature wall or a heritage room it usually does — I'd just buy Livid. The price gap on a couple of tins doesn't justify settling for a 2.9.
Whatever you land on, order sample pots and paint two coats onto A3 lining paper, then move them around the room across the day. Blue-greys like these are absolute chameleons — they go properly different under north light versus a warm bulb at night. Tape the boards up next to each other and you'll see the ΔE 2.9 with your own eyes before you commit a whole wall to it.