Unfortunately, there are some older ideas that were common in our parent's generation, and they have held on. There are some signs of change, but it is usually a cover for the racist feelings. For example, people that perpetuate stereotypes, like black men all being gangsters that don't take any part in their kid's lives, yet say they aren't racist. Or moms that say they have no problem with African Americans, yet won't let their daughter date one, or even think of dating one.
I call these people believers in the "Other" theory.
They say they aren't racist. Yet, other races are the "others," people different than them and not meant to mix with them. They can have opportunity and share a public venue, but heaven forbid they mingle with "your" group. It's the "separate but equal" policy, which didn't work the first time and isn't working still.
Yes, it's racism. Yes, your mother is racist.
The absence of racism means that you accept that we are all the same, with just a minor genetic difference that decided our skin color. It comes from evolution-our skin types adapted to where we lived-but it doesn't make us any different. At all. The absence of racism also means that you don't believe that other races are different, or need to be separate, from your own. You accept the superficial differences, but understand we are all the same beings.
Hopefully, that's you. Not racist.
But it is incredibly hard for older generations. They grew up in the Civil Rights era, and in the time after it, where race still played a very large role in society. I'm not saying race doesn't play a role now, but we can't imagine a teacher not teaching a student because she/he is black, yet our parents lived through it. So you have to take into consideration the history your mother has lived, how she was raised, and the situation she was brought up in.
Then, be thankful you were born when you were.
What can you do? Really, nothing. You can't change her mind, especially at her age. It is exceptionally hard to teach those who are racist to NOT be racist. Continue to do what you do, feel how you feel, and stand up for what you believe in. If it does become a problem down the road, for example if you decide to date someone of another race, then just be prepared to weather her comments and stand up for what you want and what you believe. That's the only way we'll ever get rid of racism.