If you've shortlisted your favorite wall colors but are having a hard time narrowing it down to a final choice, why not take inspiration from this beautiful feature wall and use them all?
Posted by Flickr member anonymous to you, this feature wall works without looking too busy because the colors all come from the same refreshing-yet-soothing palette of greens and neutrals.
You can use painter's tape to create the same effect. Just block off the squares and rectangles (note how this design uses several different proportions, while still following a logical grid) using painter's tape, then carefully roll in the desired colors, starting with the lightest-colored blocks and ending with the darkest.
(Image: Flickr member anonymous to you, licensed for use under Creative Commons)