Red is a confident colour, so the job of everything around it is to give the eye somewhere to rest. Go too bold on the partner and the whole room starts shouting. The best companions are calm and slightly muted.
Greens are red's natural complement. They sit opposite each other on the colour wheel, so a soft green woodwork or adjacent wall makes red look richer without clashing. Dulux Almost Pistachio (LRV 80.3) is lovely here — light enough to lift the room, green enough to balance the warmth. Keep it gentle; a saturated emerald would compete rather than complement.
For trim, ceilings and the surrounding scheme, lean into warm off-whites. Paint & Paper Library Sand I (LRV 95.4) is about as bright and clean as a white gets, which gives red breathing room and stops the room feeling heavy. Use it on ceilings and woodwork and you've got crisp, gallery-style contrast that lets the red do the talking.
If you want depth rather than contrast, go tonal. Mylands Alderman No.60 (LRV 58.8) is a soft, considered mid-tone that pairs with red for a layered, grown-up feel — think a deep red panelling below with Alderman above, or as a connecting colour in an adjacent room.
The "but what about" question I always get: *can I add gold or brass?* Yes — metallics are red's best friend. Aged brass fittings, warm wood and antique gold frames all flatter red walls and lift them out of anything heavy.
Practical advice: decide whether you want contrast (white trim, soft green accents) or tonal depth (mid-tones and warmer neutrals) before you buy anything. Sample all of it together on a board, prop it against the red wall, and view it in evening light — red shifts a lot under warm lamps and that's usually when you'll be living with it.