Are children colour-blind to race? Not at all. In fact, I can recall an encounter with a classmate of a different race between ages 7-10.
The pupils in my class were wondering why one of the pupils had darker skin than the rest of us. Some even questioned if she washed her hands every day and asked her to try washing off the dark colour. Why did we doubt her actual skin colour? Because we noticed that her palms were much fairer than the top of her hands, so we assumed that her palm colour was her actual skin colour. Our teacher later clarified that everyone is different and that we should learn to accept each other.
As adults, it is our responsibility to educate the children (as early as possible) about showing acceptance towards peers of various races as well as answer questions about each one anothers' race. This may help reduce unpleasant interactions or humiliating situations for the minorities.