If your character has heterochromia, which is to say if their eyes are different colors, then only one of them is effected when you become a vampire.
For instance my Breton's right is gold, & his left eye is green. When he became a vampire only his left eye changed to the black, & red vampire colors.
The right eye stayed a light gold.
I figured it was a glitch, but I wasn't certain so I made a Nord with one blue eye, & one brown. Caught Vampirism, & sure enough only the left eye changed.

Just though that it was interesting. And I guess that's out there, if anyone wants to be a vampire with extremely mismatched eyeballs.