title: Material-ui Next Theme Not applying
body: <p>I'm trying to get a simple theme override set up on my project, but it doesn't seem to be applying.</p>
  
  <p>Theme: (all it should do it change primary color to red, but it doesn't)</p>
  
  <pre><code>const theme = createMuiTheme({
      palette: {
          type: 'dark',
          primary: {
              light: red[300],
              main: red[500],
              dark: red[700],
          },
      },
      appBar: {
          height: 55,
      },
  });
  const styles = theme =&gt; ({})
  </code></pre>
  
  <p>Then I wrapped my whole app in MuiThemeProvider like so</p>
  
  <pre><code>class App extends Component {
  
      constructor(props) {
          super(props);
      }
  
      render() {
          return (
              &lt;CssBaseline /&gt;,
              &lt;Router&gt;
                  &lt;MuiThemeProvider muiTheme={theme}&gt;
                      &lt;div&gt;
                          &lt;MaterialUiApp /&gt;
                      &lt;/div&gt;
                  &lt;/MuiThemeProvider&gt;
              &lt;/Router&gt;
          );
      }
  } export default withStyles(styles, { withTheme: true })(App);
  </code></pre>
  
  <p>Yet it doesn't seem to be applying the theme to the elements in my app.  MaterialUiApp is just a wrapper for the various pieces of my main layout, such as two permanent drawers, appbar, and a content container (which currently has form elements in it).</p>
  
  <p>Edit:  I can tell the default theme is properly applying by switching my AppBar color from primary to secondary, but it uses the default theme's colors instead of my own.</p>
  
  <p>Edit:  <a href="https://codesandbox.io/s/7z52rrjmz1" rel="nofollow noreferrer">Here's the code on CodeSandbox</a>.</p>