I would try and get some books for her to bring it up in a fun way.

There is the Sesame Street "We're different, we're the same" that Mimi likes us to read to her... there are a few more that you can easily find on Amazon.com... and fairly affordable.

A few more suggestions:
- All the colors of the world
- Whoever you are
- Black is brown is tan
- The colors of us
- Black, white, just right

And some reading for you as a parent:
- I'm Chocolate, You're Vanilla : Raising Healthy Black and Biracial Children in a Race-Conscious World