actions/color.php has been heavily modified in (future) version 1.1.6.2 (see http://wush.net/trac/wikka/browser/trunk/actions/color.php, or ColorActionInfo) to correct some bugs and to allow use of background-color. When this version will be released, this action highlight will be useless (use ""{{color bg="yellow" text="highlighted"}}"" instead). Furthermore, this action reintroduces existing bugs of color action. I advise users against implementing this action, refer to ColorActionInfo instead or wait (patiently) for the 1.1.6.2 release.