Should I wear pantyhose/stockings to the office holiday party?

How dressy you should go depends on what the invitation said and where the party is being held. If it calls for being really dressed up, black hose are fine, otherwise I would go with a skin-tone. Also, if you do want to wear open-toed shoes, that is why they make sandal-foot pantyhose (with no ugly seam across the toe), so go for it if you have a great pair of open-toed shoes you want to show off.