How to redefine a message type for drupal_set_message? By default, there are 3 (status / warning and error). I will wish to add the info type, with a blue background for example. What to do?
The status is arbitrary, so:

drupal_set_message('A message', 'custom_status');


Will produce

&lt;div class="messages custom_status"&gt;A message&lt;/div&gt;


Notice the "custom_status" class, which you can target with CSS.