Gringa status: please confirm

Today as I was getting on the bus back to site, the teenage boy loading my pack into the trunk asked me, "¿usted es gringa?" ("are you a gringa?"). I looked at him and burst out laughing: "en serio, did you just ask me if I'm a gringa?" The bus driver (his boss) quickly told him that it's not exactly polite to just ask people if they are gringos, but I kept chuckling and assured him it was fine - I was just taken off guard because I literally had never been asked that question before. In my opinion, it is muy obvio that I'm a gringa - I've met approximately zero Peruvians with pale freckled skin and green eyes. People ask me all the time if I'm from the United States or if I speak English, but never have I been asked to confirm the basic fact of my gringa-ness. But there's a first time for everything, especially in Peace Corps.