I'm half white and half hispanic, so why do most people ume I'm from Mexico?

I have nothing against Mexicans. I have nothing against white people. My dad's roots were French and German. My mother's roots are from Mexico, and from Yaki indians. However, people just see my olive skin and ume I'm from Mexico. I live in an area where there are mainly white people, I work with nothing but white people, and I am totally okay with that. In school, I had problems with racism from other students. At work, my co-worker was talking badly about Mexico, and immediately whipped her head towards me and said,"NO OFFENSE, GINA!" I responded,"I'm not from Mexico." And she said,"Well, you are STILL hispanic!" and while I am part hispanic, I feel like Mexico's problems aren't mine, I have never stepped foot on Mexican soil. Even if I was Mexican, why should their problems lie on my shoulders? Everuone in the car when my co worker said that was laughing and I was so upset. I felt like she just said that to be rude. I am not ashamed of what I am, nor am I proud. How can I be proud when I accomplished nothing by being born with my olive skin color? I like my skin color, because I never have to tan. But others judge me on that color. I'm just as much "white" as I am "dark" and even if I wasn't, it upsets me people judge so harshly based on a color of skin.