The door was the beginning: it was first to turn black.
In its previous life my space was a serviced apartment—and the door made this abundantly clear. It had a no-smoking sticker, an automatic door closer and (no doubt) hundreds of fingerprints from travelling strangers.
Having removed the tiles and polished the concrete floor (more on that later), I was left with a decent gap under the door. I found a brass door seal that matched the brass switches. It took a bit of hacksawing and screwing but it works just fine. The black is the same excellent purple black as the black wall. And there are no fingerprints to be seen.
details: paint: dulux klavier, brass door seal
cost: paint $50 (with plenty left over), seal $20