Vanitas looks like a palette swap of Sora, with black hair and yellow eyes. His outfit mimics Riku's Dark Mode, a red and black bodysuit with a skirt in the back. His mask is predominantly black, with red trim.
Vanitas Sentiment has a black and white version of Vanitas' outfit.
 Journal Entries
 Kingdom Hearts: Birth by Sleep
 The Masked Boy
A mysterious figure with ties to Master Xehanort. He warned Ventus that Terra was in some kind of danger, but disappeared before explaining any further.
A mysterious boy who hides his face behind a mask. He has ties to Master Xehanort. Vanitas warned Ventus that Terra was in some kind of danger, but disappeared before explaining any further.
Related ThreadsWhy Vanitas and Sora look alike??? - last post @ Oct 18, 2018
vanitas and secret boss(spoiler) - last post by @ Jul 20, 2011
Share your experience in battling VANITAS - last post by @ May 20, 2014
Vanitas - last post by @ Feb 21, 2011
Has there been any Vanitas concept art? - last post by @ May 18, 2010