Any of these rooms would look fine, even good, with neutral walls, but the simple addition of bold, blue paint takes them into seriously stunning territory.
Why blue? Blue's cool tones mean you can brighten it up without it looking garish, and since it works with so many other colors, it's great on a big area like a wall. From robin's egg to peacock to navy, a bold paint is the quickest and easiest way to liven up your decor.
(Images: As credited above.)