Red 03 is a dusty, blushed red — gorgeous, but it needs handling. The single biggest mistake is sticking brilliant white on the woodwork next to it. Don't. Brilliant white reads cool, and that cool cast drags Red 03 towards mauve, which is exactly where you don't want it to go.
Instead, pair it with a warm off-white on skirtings, architraves and the ceiling line. That keeps the red looking like a proper soft terracotta-red rather than something purplish and sickly.
For a contrast colour, Dulux Almost Pistachio (LRV 80.3) is a cracking shout. It's a pale, dusty green that sits opposite red on the wheel, so it brings life without shouting — perfect for a connecting hallway or the inside of a recess. Light enough at LRV 80.3 to keep things airy.
Want something with a bit more weight and tailoring? Paint & Paper Library Slate IV (LRV 67.5) is a softened blue-grey that cools the scheme just enough to feel grown-up. Use it on a feature joinery piece or an adjoining room.
And for the deep, anchoring accent — Mylands Cigar BH.20 (LRV 11.8) is the one. A rich, dark brown-red that picks up the plummy undertones in Red 03 and grounds the whole scheme. Brilliant on a single door, a built-in bookcase, or carried through in upholstery and rugs.
The metalwork matters more than people think here. Antique brass and faded oak warm Red 03 beautifully — think aged brass switch plates, oak floors, leather. Chrome and polished nickel chill it and tip it towards that mauve again, so keep them out.
Practical advice: get a Lick peel-and-stick of Red 03 up alongside your warm white and live with it for two days, morning and night. Pinks and dusky reds shift more than almost any other colour with the light, so judge it in your own room, not in the shop.