Three friends, Alan, Bob and Cecil, sit down at a park bench. Each of them is a Knight or Liar and each knows what the other two are.

Forgetful Bob, well known for his flamboyant hats that are either red, white or blue, asks Alan: "What colour hat am I wearing today?"

Alan replies: "There is a chance Cecil would tell you it's blue. If you saw it, there is a chance you would say it is white."

Bob sighs, "I should have asked Cecil - he always tells me the truth..."

What colour hat is Bob wearing?