You can create template copy , in j16+ duplicate option, set colors in second then apply second only on home page in template assignment.
For j1.5 it's little bit harder, you have to create copy manually . First copy whole template folder to temporary location. Then modify template folder name and all template files to use new name. Simplest is to just replace appearance of word "cosmetics" with "cosmetics2" After that you need to pack that and install it in joomla like new template. Set settings for it and then use template assignment to assign it to home page.
Solution 2 for j15 : open index.php of template modify boddy tag like this:
<body>
to
<body <?php echo ( $ishome ? " class='home' " : ""); ?> >
then use .home .... to target css rules for home page