If you're worried about trying something different on a large expanse of wall, experiment in a small space. Instead of painting the living room forest green, try doing the laundry room first. Or experiment in the guest bedroom where you don't go all that often.

Another possibility is to concentrate on something that normally doesn't show. Paint the back side of a bookcase or the inside of a cabinet so you can see what the color looks like on a decent expanse before you commit to a whole wall.

Deep colors such as purples and reds may take as many as four coats to evenly cover a white wall. Be prepared for that when your painter gives you an estimate in Mill Valley, California.