Style Every Other Widget

I’d like to have different classes for widgets on a dynamic sidebar so I can alter the css – e.g.

First widget gets ‘before_title’ => ‘<div class=”widget-title”><h3>’ then the second one gets ‘before_title’ => ‘<div class=”widget-title2″><h3>’

Does that make sense and if so can anyone point me in the right direction?

I’m guessing I need to pass a parameter with widgets_init but I’m struggling to work out exactly where this called.

Any and all guidance appreciated.