Why are so many of the sith red and tattooed, no matter what species they are, and if theyre not red and tattooed then they are part cyborg. Very few appear to be otherwise.

One way or another, the Dark Side is a corrupting influence.  They want to be feared, and a disturbing visage is certainly a step in the right direction.
 
Occasional duels with a Sith-hunting Jedi (or other organization) can certainly lead to the regular loss of body parts.  It's tough being evil, sometimes.

" @MrMiracle77: That makes sense, but i still dont understand the red, i know the black are tattoos but their skin is red no matter the species which strikes me kind of odd "