You sure it's because you don't date outside your race of because she just not the right type of girl you would date who happens to be outside your race?
If you serious then just tell her its always better than making some shit up. Trust me bro don't feel bad we all have different preferences. There aren't many white girls I'm really attracted to. And I don't really give too much thought on dating straight up Africans either. It's even some black girls I don't rock with. I can't stand a ratchet ass black girl. A little rachet? Yea that's cute, but **** all that other bullshit.
Ima keep it 100 with you I like what I like. But I can't say I wouldn't date a white girl or black girl or African, Indian, you get the point, because I know there are some attractive ones out there, and if I can be attracted to them, then I probably would consider dating them depending on the circumstances. Repeat after me. "I am a man, and I have preferences. I'm attracted to certain things, some more than others. Nothing against you, I just not attracted to you." Nothing racist about that.
Now this is why I asked you are you sure you don't date outside your race? Because if you feel more like what I mentioned earlier, you can use that quote and wouldn't need to explain yourself. But if you really are against dating someone simply because they can be considered "outside of your race", then just know I'm praying for you fam. It is not gonna be pretty when you tell this chick that