Interracial Dating

I'm almost 18 and my parents have always told me to only date people of my own race. I usually don't tell them about the people I'm dating because I don't want the trouble, so when we go out I just tell my parents that we're best friends. But even my first relationship and my first kiss was with someone of a different race when I was 14. Since then, I've dated people from 3 other races, and I have dated people from my own race too. I don't see any difference? It doesn't feel any different?When I ask them why, the only thing they'll say is "it's just what we belive is best" and that's it. So maybe some of you could explain why my parents might not want me do be with any other races.