That's a little different. With the exception of lighter skin, Armisen bears a passing resemblance to Obama. He has dark hair, is fairly dark complected - and I believe, is part Latino. In fact, I just googled some pics of him playing Obama and I don't think they put any dark make-up on him.
Armisen did wear "darker makeup" when he played Obama, at least during the campaign and in the first few months of the show:
http://www.washingtonpost.com/wp-dyn/content/article/2008/02/28/AR2008022803988.html