I'm going to ask a girl if that's her natural hair color?
Why would you be that rude and ask such a question about the girl's hair color?
I've been curious since the day I met her.
While it is always a question of curiosity about real hair color, females still prefer not to be asked about it. We find it to be very inappropriate.
It's too late, I think I already offended her.
Well, she definitely wouldn't tell you now if you already offended her. You should apologize to her and avoid the hair color question altogether.