A very ugly style is hardcoded into the scw_js.php data calendar javascript.
It'd be trivial to replace the two big document.writeln's containing the CSS with this:
document.writeln('<link rel="StyleSheet" type="text/css" href="<?php echo JB_THEME_URL; ?>scw.css" />');
and include the entire CSS in your favourite theme directory in a file "scw.css".
Perhaps you can do a function instead of the the JB_THEME_URL bit so users who actually like the default style can just leave the scw.css file unchanged in the default theme directory.