From a sales rep with 7+ years selling ads for a weekly newspaper.
"I want you to use the extra white ink in this ad"
Upon telling her that we do not use "white ink" in the newspaper - ever, she gets a "I know more than you because I have been here longer look" and asks "well, where does all the white in the paper comes from then?".
I had to show her a roll of newsprint to get her to understand that it was simply the paper color without ink on it that was white.