In the normal life state, servos will have green eyes and servettes will have blue eyes. The green is for plot related reasons, and the blue is just because that's the original default servo eye color.
Vampires have red eyes as usual, with the vampiras getting a black bow and red lipstick.
Witches and warlocks get stars on their cheeks and purple eyes with sparklies in them, with the witches getting purple lipstick.
Werewolves have yellow eyes with little moons in them, with the she-wolves getting a black bow with black lipstick. Were-servo transformations are very glitchy. Ideally, they should be normal during the day and take on the yellow eyes every night at 8, but sometimes they don't. If this happens it might help to change them into their formalwear. Also, in some cases, exiting the lot and going back into it will also make the yellow eyes show up.