Sang de Boeuf is Edward Bulmer's deep oxblood — a properly atmospheric red that wants to be drenched. My honest advice: don't fight it with a feature wall. Take it across walls and woodwork together for an enveloping evening room — a dining room or snug — and let it do the heavy lifting.
The partner colours all need to lean warm. The single most important rule: avoid cool whites. Anything with a blue or grey undertone turns this red muddy and lifeless. Go for a warm stone off-white instead. Paint & Paper Library Sand I (LRV 95.4) is bang on — a soft, creamy near-white that's perfect above a dado rail, lifting the room without breaking the warmth. Pair it with old oak, antique brass fittings and a bit of patina and you're well on the way.
For a second accent, soft sage green is your friend — red and green are natural complements, and a dusty, knocked-back green sits beautifully against oxblood without going Christmassy. Dulux Almost Pistachio (LRV 80.3) is light and chalky enough to feel fresh on a ceiling or in an adjoining hallway.
If you want to deepen the scheme rather than lighten it — say for joinery, a study or a tonal layered look — Mylands Alderman No.60 (LRV 58.8) is a handsome mid-tone that holds its own alongside the red without competing.
The "but what about" question I always get: can I use crisp brilliant white woodwork? No. It'll look stark and cheap against this colour and emphasise every flaw. Stick to the warm off-white throughout.
Practical bit: test Sang de Boeuf large and live with it under lamplight, because reds like this come alive in the evening and can read heavy in flat daylight. Two coats minimum, and a tinted undercoat will save you grief getting even coverage. Get your lighting warm — 2700K bulbs — and this room will feel like a hug.