Unfortunately, this little girl was only repeating what she had been taught at home. Kids this young don't come up with ideas unless their parents plant the idea in the first place.
the only tactic I've tried is to answer the child honestly and without becoming upset. My hope is that by hearing the other side of the issue, it might make an impact, but I doubt it.
The parent is responsible for this child's conduct, and I'm sorry your daughter had to hear it. I'd tell her honestly that there are people in the world who don't respect others...but that you love her no matter what color she is, or what color you are.
Kelley