The accusation has been made that God was racist when He commanded Israel to destroy the people of Canaan in The Old Testament
The problem is that it is rather hard to be racist when both Israel and Canaan were of the same race. The two nations descended from Shem and Ham, two brothers with the same parents, as described in the genealogies back in Genesis 10-11.
To claim racism in such a situation reinforces the theory that atheists and critics pass around proof texts without really reading the story of the Bible and finding out what is going on (For more, see here). At a minimum, they are more interested in finding critical faults than in discovering what the text actually says.
Christianity is not racist, for it teaches that all humans are of the same race: the human race. What is actually racist is evolution, which says that all physical and mental differences are due to evolutionary processes, and must therefore maintain differences between people groups. For more, see here.