Photo: Joe Brusky On a typically warm and sunny Saturday last week in Venice, California, Kristie Mitchell sat outside at a table surrounded by Sharpies and a pile of posters. Each one featured the same basic illustration – an outline of an African-American woman and three school-age children with the words “I Stand For” across the top. It was up to Mitchell and the other public school parents and children around the table to decorate the poster with whatever color…