Multi-racial four year old - discuss race?

I have a four year old who is half Latino and half caucasian. I have never discussed race with her - but a teenaged Latino cousin told her she was "white". My dark haired daughter also talks about wanting to have blond hair. A friend her age already is throwing around names of categories for people, saying he didn't want to be the black boy in chutes and ladders because he wasn't black. I was surprised. I don't know what's appropriate to say - I can't talk about melanin in skin, she won't get that. Is this really something I should talk to her about?