My living room is carpeted in plain beige, but I love colourful area rugs. Can I layer one over my carpet?
Carpets are made to be layered, especially beige ones. Layering gives a room depth and the appearance of size, and it's a warm statement in winter, much like a fur vest. I think of beige carpets as neutral bases, similar to hardwood. Preferably, you'd layer a low-profile, wool-sisal carpet on top of hardwood, leaving a one-foot perimeter of exposed wood. The tough thing about wall-to-wall carpet (hopefully yours is low-pile) is that it collects dirt near the edges and doesn't always sit flat. If that's the case, you can install a hardwood border around the room.
Then you can bring on the colourful carpets – my favourite right now is an over-dyed, silk Persian rug in purple, pink and turquoise. As for placement, I like to have the feet of the sofa and chairs just hitting the edges of the carpet. Don't waste all that beauty under the furniture.