Boyish blue and girly red?
There were two siblings - Alfred and Brenda. One of them likes red while the other likes blue. Also one of them always tells the truth the other always lies. Unfortunately you don't know who is the truth teller and who is the liar.
Imagine you want to know who likes which color. You are allowed to ask Alfred and/or Brenda for the answer. What is the fewest number of questions you need to ask?