After a while my light skin vamps just turn a almost sickly green color but sometimes the sim doesn't in some saved games....normal?

Maybe it helps if you show some screenshots.

My vamps were more gray, but then I decided to turn off advanced rendering which got rid of the glow altogether. When I updated the driver for my graphics card the settings were reset (so advanced rendering came back on) and the vamps appeared more green.. but the reset settings had lower sim quality settings than what I usually like to have, so maybe it has something to do with that, have a play around with the quality settings.. Or even try updating your driver.

Are they vegetarian vamps? Ah, just kidding. I think part of it depends on the sim's original skin base before they got vampified. Then it's up to your graphics on how it shows up.

My system shows vampires always as slightly greenish, but the visual override that causes this is not always persistent and they can switch back to their default colour from time to time. Maybe your vampires suffered from this in the beginning and the override just kicked in recently.
I had this happen when I placed a vampire from the Bin via Edit Town, he ran around the world for several days without his vampire hue.