Different colored widgets?

I mading a new theme which widgets ready and widgets colors must be like k2’s comments.
I try this but not works.

array(
                'before_widget'=>'<li id="%1$s" class="%2$s">',
                'after_widget'=>'</li>',
                'before_title'=>'<h2 class="widgettitle">',
                'after_title'=>'</h2>',
                  ));

The output must be like this:
<li id=”widget 1″ class=”1″>xxx…
<li id=”widget 2″ class=”2″>yyy…
<li id=”widget 3″ class=”3″>zzz…
Thanks for your help.