BuddyPress.org

You can deregister the admin bar CSS and then load your own CSS.

Something like this:

function custom_remove_adminbar_inline_styles()
{
	if ( !is_admin() ) {

		remove_action( 'wp_head', 'wp_admin_bar_header' );
		remove_action( 'wp_head', '_admin_bar_bump_cb' );
                wp_enqueue_style( 'wp-adminbar-custom', get_template_directory_uri().'/css/adminbar.css', false, '1.0', 'all' );

	}
}
add_action( 'wp_head', 'custom_remove_adminbar_inline_styles', 9 );

Then in your theme you would add /css/adminbar.css and make it look however you want. You can copy the adminbar from WordPress as a starting point.