I'm not sure what colour to paint my living-room chair rail. Should it match the walls or the trim?
Try one of two approaches for two very different results. If you paint the chair rail the colour of the trim, you will get a horizontal band 30 inches or so above the floor. Putting a darker colour below and lighter one above will make the wall appear taller. This is a tried-and-true approach.
Alternatively, painting the chair rail (and trim) the same colour as the wall will create a striking monochromatic effect. If you keep the colour neutral and pale, the walls will simply fall away. Darken up the floor and paint the ceiling a chalky blue-white and your furniture and accessories can be as bold as you like. Keep the drapes the same colour as the walls and decorate with black and white framed photographs for stage-like drama. If you don't like the effect, you can always repaint your trim and chair rail a contrasting shade, knowing that at least you tried living on the edge.