Image Color Dominator picks a small three-color palette based on an input image. Similar to iTunes 11, except orders of magnitude slower.
For an example, let’s take this image of Mars.

At the time of writing, the current version of Image Color Dominator selects the following colors:
Background color: #010000
Foreground colors: #C26A44 and #D2C4C9
Full write-up: Image Color Dominator
Source on Bitbucket: https://bitbucket.org/epb9000/image-color-dominator