"Of course I knew." Those words come out in a bland, disinterested tone, his gaze shifting aside. Since she's already moved back onto the topic of the pie, he returns to it quickly. "Mm. The blueberry pie was good."

To be honest, he half-expects her to follow that up with 'is that why your skin is blue?' If it happens, it happens. If not, well... he's going to see how naive and gullible she winds up being. It's not like blue skin is harmful, so it's just a minor troll.