not straight forward, as the individual items in the category list don't have individual css classes to style them with.
try to add a filter function to functions.php of your theme; for instance:
add_filter('the_category','the_category_css_class');
function the_category_css_class($output) {
$list = explode('" title',$output); $output = '';
$len = count($list)-1; $i=0;
foreach( $list as $list_item ) {
$cat_slug = explode( '/', $list_item);
$cat_slug = array_reverse($cat_slug);
$output .= $list_item;
if($i < $len) $output .= '" class="cat-' . $cat_slug[0] . '" title';
$i++;
}
return $output;
}
this would add a css class, such as .cat-term-slug to each list item;
example:
say your category is 'Social Media' - then the term slug is 'social-media' - the filter would add the css class '.cat-social-media'
style with:
a.cat-social-media { color: green; }
for further category dependant styleing, you could try and use post_class() in the post div; and body_class() in the body tag:
http://codex.wordpress.org/Template_Tags/post_class
http://codex.wordpress.org/Template_Tags/body_class