title: Is it possible to add a custom hover color to Raised Buttons?
body: <p>Working on a project that is using the Material-UI library of components and I've gotten a request for a custom button hover color that is outside of the normal convention of the MUI theme.</p>
  
  <p>I found this relevant block of code in the Raised Button source, <a href="https://github.com/callemall/material-ui/blob/master/src/RaisedButton/RaisedButton.js#L98" rel="noreferrer">https://github.com/callemall/material-ui/blob/master/src/RaisedButton/RaisedButton.js#L98</a>. Setting a custom labelColor does change the hover state, but that still does not satisfy my current need to have the button hover color something different than that of the label color.</p>
  
  <pre><code>overlay: {
    height: buttonHeight,
    borderRadius: borderRadius,
    backgroundColor: (state.keyboardFocused || state.hovered) &amp;&amp; !disabled &amp;&amp;
      fade(labelColor, amount),
    transition: transitions.easeOut(),
    top: 0,
  },
  </code></pre>
  
  <p>Is there a way to override the overlay background color some other way so that I can use a separate custom color?</p>
  
  <p>To clarify I'm looking to do this using inline styling or through overriding a prop on the button.  Appending a class and using external CSS is not an option.</p>