table headers without specifying class would get the default colgroupb would be used if there were adjacent groups only the table headers would need to be set apart, not the table cells I didn't use the html tag since it doesn't seem to work in FF1, but does in IE6 pick any colors, I've just picked these because they contrast with .alternate CSS: th.colgroupa {background-color: #ddd} th.colgroupb {background-color: #ccc} From link-categories.php: