My oldest dd is almost 4, still very young. But for our family, race is no big deal. She knows that Daddy is from India, and Mommy is from America. Daddy is brown, Mommy is white. She proudly calls herself "Indian American." And she can find India on a map. (We've traveled there, but she's too young to remember.) DD herself looks white, like me. Her little sister, 18 months old, looks more like Daddy (actually she just looks like she has a very nice tan).
Also, one of my brothers is married to a woman who is Chinese. So dd also knows that she has "Chinese American" cousins. And we've shown her China on a map. When we make Chinese stir-frys with rice, we tell her "This is what people eat in China!"
For our family, it's not so much a matter of race, as a matter of where people come from in the world. I know that geography is still very abstract for a 4-year-old to understand, but still we talk about it. We have a globe, she loves to look at maps. She asks "what country is this?" etc. We have movies of India, she loves to watch them with us. I love to watch travel channel on TV, and sometimes I'll tell her, "look, that is Spain!" Or "that is Africa. Giraffes live in Africa" (she loves animals).
So for us, race is really just about people coming from different places around the world. Just as she learns that the mangos we eat grow in warm places, like India and Mexico, etc., or that people in India and China eat a lot of rice, whereas people from Europe eat a lot of bread, etc. The question of race fits in with the broader understanding of the world.
Skin color is not so much an issue. People who come from different countries look different, that's all. I hope my children grow up with an appreciation of different places. Really, it's fascinating to learn about geography, history, etc. We're not afraid to address race in our family. It's a fact of life. Underneath their color, people are the same everywhere. It's this understanding that we will try to instill in our children.