I don't know, of all the places to find the last background colour declaration in the forum posts, and you're not going to believe it, it was in the following files: groups/orca/layout/base/xsl/forum_posts.xsl groups/orca/layout/base_en/xsl/forum_posts.xsl groups/orca/layout/uni/xsl/forum_posts.xsl and groups/orca/layout/uni_en/xsl/forum_posts.xsl. You need to look for : <div id="f_tbl" style="background-color:#ffffff;">