To prevent duplicate IDs in hook_field_formatter_view

Hi,
with the default implementation of hook_field_formatter_view, we unfortunately got duplicates id attributes. To prevent it, I suggest to use a class attribute instead of id. And to limit inline css duplication, I suggest to use drupal_static, as it follow :

function jquery_colorpicker_field_formatter_view($entity_type, $entity, $field, $instance, $langcode, $items, $display)
{
    
    $css_attachment_cache = &drupal_static(__FUNCTION__ . '_css');
    if (!isset($css_attachment_cache)) {
        $css_attachment_cache = array();
    }

	$element = array();
	foreach($items as $delta => $item)
	{
		if($display['type'] == 'jquery_colorpicker_color_display')
		{
			$element[$delta]['#markup'] = '<div class="jquery_colorpicker_color_display_' . $instance['id'] . '_' . $delta . '_' . $item['jquery_colorpicker'] . '">&nbsp;</div>';
			
			$css_attachment = array
			(
				'type' => 'inline',
				'data' => '.jquery_colorpicker_color_display_' . $instance['id'] . '_' . $delta . '_' . $item['jquery_colorpicker'] . '{background-color:#' . $item['jquery_colorpicker'] . ';}',
			);
			if(!in_array($css_attachment, $css_attachment_cache)) 
			{
    			$css_attachment_cache[] = $css_attachment;
    			$element[$delta]['#attached']['css'] = $css_attachment_cache;
		    }
		}
		elseif($display['type'] == 'jquery_colorpicker_text_display')
		{
			$element[$delta]['#markup'] = '<div class="jquery_colorpicker_text_display"><span class="jquery_colorpicker_hash_mark">#</span>' . $item['jquery_colorpicker'] . '</div>';
		}
	}
	return $element;
}

It's working well in my installation. Can you give me your opinions ?
Thanks!