isc-category-body-classes.php

<?php

// includes/classes/class.category.php. Add before:
// $GLOBALS['ISC_CLASS_TEMPLATE']->SetPageTitle($this->BuildTitle());

$bodyClasses = '';
$parents = explode(',', $this->Data['catparentlist']);
foreach($parents as $parent) {
	if(!trim($parent)) {
		continue;
	}
	$bodyClasses .= ' category'.$parent;
}
$GLOBALS['ISC_CLASS_TEMPLATE']->assign('BodyClasses', $bodyClasses);

// In template/category.html, class="%%GLOBAL_BodyClasses%%"
// Will give you, for ex: class="category1 category3 category4" (assuming current category is 1 > 3 > 4)