it's not that sophisticated as all the php-code above... but why not adding for example:
<link rel="stylesheet" type="text/css" href="/wb/templates/css/dark.css" media="screen,projection" />
in the WYSIWYG module of a page (paste in code-view....) and on the other child-pages duplicate the (dark-css)
module-section with the section-picker module... do the same with the other css (color) files...
so another WYSIWYG-section on a other page etc etc... this work... no matter what code... and takes
maybe 15 minutes (without a cup of coffee...)
or check out my Template Framework 3 Lite (demosite.vanallerle
i.com) (it uses another technique) with handeling Css files and Vars,