Warning: Material-UI: The white color was not parsed correctly, because it has an unsupported format (color name or RGB %). This may cause issues in component rendering.

javascript 
const muiTheme = getMuiTheme({
  raisedButton: {
    textColor: 'white',
    color: purple900,
  }
});

こんな感じにMaterial-UIの色を変えて遊んでたらエラーが出た:

Warning: Material-UI: The white color was not parsed correctly,
  because it has an unsupported format (color name or RGB %). This may cause issues in component rendering.

ヘックスコードに変えれば問題はない:

const muiTheme = getMuiTheme({
  raisedButton: {
    textColor: '#ffffff',
    color: purple900,
  }
});

参考: https://github.com/callemall/material-ui/issues/6781