Does coffee make your teeth yellow?

Yes, nicotine inhalers do stain your teeth because just in general nicotine stains your teeth. If you don't like getting your teeth stained, I wouldn't try nicotine inhalers!

There is no tar in a tobacco-free product like all or at least most electronic cigarettes. I understand that nicotine by itself is colorless. Most discussions of the effects of nicotine assume that it is always used in a form containing the entire spectrum of substances found in cigarettes, so you have to be analytical about what the person posting is likely describing.