Well it looks likes its hard coded in the /forum/clientscript/jquery/jquery.mobile-1.0a2.min.css file
But the file is a mess and I can't really make heads or tails of it, its similiar to the jquery one
http://code.jquery.com/mobile/1.0a3/...bile-1.0a3.css
but I can't tell where to edit. I want to change the category background colors from that light blue one to another color.