The colour scheme refers to all the colours you can see in a room. They should all work well together. Just having one colour that doesn’t fit can ruin the whole scheme, so don’t ignore that one colour. It could be present in the wallpaper, the flooring, a stained glass window etc. If you don’t intend to remove the colour, you need to make a new colour scheme that will work with that colour.
The pink accessories in this room were dramatic with the black and grey sofas, but the home-owner hadn’t taken into account the fact that the walls had a golden background. Pinks and golds don’t work together, so the room felt wrong. Just swopping the pink for gold made the room glow.
So, when chosing accessories for a room, don’t forget the colour of the wallpaper!