I don't know about his attitudes toward blacks, but he was a notorious Indian-hater. I posted the piece on Baum to warriornet, after this appeared:
"The peculiar policy of the government in employing so weak and vacillating a person as General Miles to look after the uneasy Indians, has resulted in a terrible loss of blood to our soldiers, and a battle which, at best, is a disgrace to the war department. There has been plenty of time for prompt and decisive measures, the employment of which would have prevented this disaster.
"The PIONEER has before declared that our only safety depends upon the total extirmination of the Indians. Having wronged them for centuries we had better, in order to protect our civilization, follow it up by one more wrong and wipe these untamed and untamable creatures from the face of the earth. In this lies safety for our settlers and the soldiers who are under incompetent commands. Otherwise, we may expect future years to be as full of trouble with the redskins as those have been in the past.
"An eastern contemporary, with a grain of wisdom in its wit, says that `when the whites win a fight, it is a victory, and when the Indians win it, it is a massacre."
-- L. Frank Baum
Louis Proyect (http://www.panix.com/~lnp3/marxism.html)