Where are you getting this from?
I've studied Olmstead at length and have never come across anything to suggest anything bigoted about his thinking or his approach. On the contrary, He saw parks as a democratizing and civilizing agent in cities. On slavery, he saw the practice as "morally odious" and was an anti slavery activist.
Here is a passage from Wikipedia:
"The design of Central Park embodies Olmsted's social consciousness and commitment to egalitarian ideals. Influenced by Downing and his own observations regarding social class in England, China and the American South, Olmsted believed that the common green space must always be equally accessible to all citizens. This principle is now fundamental to the idea of a "public park", but was not assumed as necessary then. Olmsted's tenure as park commissioner in New York was a long struggle to preserve that idea."
Am I reading the pasteurized versions of history books? I sincerely hope you are mistaken.
**I found some original texts and quotations by Olmstead himself, and I have to conclude that to call Olmstead a bigot is false.