Paint colour looks completely different on a tiny chip than on a whole wall, which is why so many people end up repainting. A little testing prevents an expensive mistake.
Test large samples
Buy sample pots and paint big swatches — at least a couple of feet square — on different walls, or paint poster board you can move around. A colour shifts with the wall it's on and the light it's under.
Watch the light
Natural and artificial light dramatically change a colour. Look at your swatches in morning, afternoon, and evening light, and under your actual bulbs. North-facing rooms read cooler; south-facing warmer.
Mind undertones and flow
Greys and whites have undertones — blue, green, pink — that show up large. Hold candidates against your flooring and fixtures. For an open plan, choose colours that flow room to room rather than clashing at every doorway.