OS Open Map Brinjal style
It's dark. It's brooding. Is it bruised? No, it's a simple dark rendering of the Ordnance Survey's Open Map Local product. The style sheets were created in QGIS and are available from Github.
I only used the roads, buildings, surface and tidal water layers, and a very muted styling of the woodland areas to build up the map. I think it would be a good base to use for overlaying brightly coloured datasets as a counterpoint to darkness. Make your data shine!