Date: 02/17/06 (PHP Community)    Keywords: php

Need a color scheme? You can drop a couple of colors you like into this page, and it will create some more by mixing the two. Note that the more similar the parent colors are, the more similar the child colors will be to each other and to them. (Enter 000000 and FFFFFF--or any single color twice--for the extremes of this phenomenon.)

The code for that is in the usernotes for image functions on php.net.

Source: http://community.livejournal.com/php/415852.html