Krayt is possibly human. We don't know for sure. Darth Stryfe is also human, but we haven't seen him yet, other than the preview in Legacy #0.
At the Battle of Ossus, there were about five or six Human Sith, a Gotal Sith, a Mantellian Savrip Sith, a Quarren Sith, a Zabrak Sith, a Twi'lek Sith (not Talon), and then Darth Nihl. Kol Skywalker killed most of them, seeing as Nihl appears to be the last one standing.
There was a Zabrak Sith among the fallen, as seen when Kol Skywalker dies and falls into the pile of dead Sith bodies.
However, I think for the most part they are all Human. According to Duursema, the only Sith that might be naturally red is Darth Talon, the Twi'lek. The rest are all tattooed Red and Black.
Must be noted, Maul's skin is not red before the tattoos. Zabraks have brown skin, as seen with Eeth Koth, Agen Kolar, and now Wolf Sazen.
And check here in the PT section. Comics Downloading Thread Thing... Should take you to the post with a link to Legacy1.
http://www.geocities.com/davidayton/CDisplay
Use this link.