Interesting ..just looking around my lounge and the only black is the telly and the black soot in the fireplace ..not sure that counts :)

It doesn't have to be black, but things work when there are a mixture of tones (imagine everything photographed in black and white). A room could be very colourful but if all of the colours are similar tonally then it will look flat. Similarly, an interior which has pale floors, walls, ceiling and furnishings will look boring until something dark is introduced. Black is the obvious but it could be a rich teak wood against a white backdrop. The current trend for pared down Scandi interiors often exemplifies this perfectly.

Colour tones is something I don't quite get ..colour is such a massive subject ..seems easy when you start then putting things together you realise how much of a skill it is to do it right.