Echo one colour already in the room rather than matching everything, keep the whole room to two or three colours, and let the artwork be the most saturated thing in it.
The instinct is to match the sofa. Matching is what makes a room look like a showroom, and it dates fast.
Echo, don't match. Pick one colour already present — in a rug, a cushion, the wood of the floor — and choose work that contains a version of it. Close but not identical is what reads as considered.
Two or three colours in the room, total. Count what is already there before you add. A room with four strong colours cannot absorb a fifth, however good the artwork is.
Let the art be the most saturated thing. In a room of neutrals, the artwork is where colour is allowed to happen. That is why rust, teal and ochre work so well against grey, linen and pale wood: they are warm enough to carry the room without shouting.
Cool rooms, warm art. North-facing rooms get blue light most of the day. Warm work — ochre, rust, sand — compensates. South-facing rooms can take cooler work: teal, grey-green, mist.
Wall colour matters more than people expect. On a white wall, almost anything works but nothing is flattered. On a soft greige or clay wall, work with warm ground colours looks like it belongs to the room.
Test at the right size. A colour that is pleasant at postcard size can dominate at a metre wide. Look at any piece at true scale in a room before deciding — that is what the room preview on each artwork page is for.