http://img694.imageshack.us/img694/1840/odd.png Note that the tailor is much "whiter" than the PC. She looks the same with armor on as the PC does. (before you ask why, I noticed the dress she had was unique, and being a perfectionist, baneful gauntlet+loot+resed it off her). I haven't seen any other NPC look pale like that (but not every NPC has unique armor I steal). This is not the lighting, I checked. I also noticed a few NPCs have pink underwear, most noticeably the brothel workers in Tyrant, but also Cynthia Boggs if you equip+unequip armor on her. Any idea what is with the alternate colors?
Although you're asking as a player and not a modder, here's the low-down on why milady is so pale: It's an option you can select when you place a character. Place the base character (Human female, for example), then right-click the figure and select edit. From there you can select from a wide range of possible skin tones, already-applied clothing, or even change the race and gender.
She's sort of greenish to me. It can be assumed that her outfit hides her Bride of Frankenstein background which became apparent once you removed said disguise. As rroyo said, when placing npcs you can choose a variety of tones. There's four different versions for each sprite I think.
Indeed, the Black Root tailor is green. The Halfling Priest at the isle of Despair is green as well, and so is... Actually those two are the only green humanoids I recall, at least at the moment.
Hm... I wonder how many sprites in vanilla are like that? Barring the naked halflings from the Isle of Despair (creepy little podgers. Remind me of the school from Silent Hill), I've never seen any others like that. I've used green median sprites to represent particularly unfortunate half-orcs, but never seen them used for that reason, or any other, in the game itself.