Man, at that point the franchise was 10-12 years old out here; HOW does someone go that long without knowing what color Pikachu is??? If it was '99-00, the Regis era, I could maybe see it since it was so new; but after a decade? How was he so sheltered?
The explanation for this, I believe, would be that the contestant was not a video game player, or even a parent of one. Pokémon is a children's franchise, and is meant to have kids for its fanbase, not necessarily adults.
Plus, that is VERY easy and well-known for a question worth $16,000. The audience would have almost all easily voted for B, Yellow, as the correct answer. And the contestant probably had a phone-a-friend who knew of Pokémon.