Hardest Riddle Ever.?

Two friends have a bet. Boy A says Big Bird from Sesame Street was yellow since the start of the show. While Boy B says that Big Bird actually started out as grey. As we all know, Big Bird has always been yellow yet through a loophole Boy B won the bet. How is this possible. PS there is a legit answer to this riddle. Give me your thoughts and check back for the answer if you're curious, it's a good one. :P