title: material 2 paletta contrast color
body: <p>In the paletta, I can see contrast.
  How can I choose a contrast color?</p>
  
  <p>works:  </p>
  
  <pre><code>scss
  mat-color($button-primary);
  </code></pre>
  
  <p>Not working  </p>
  
  <pre><code>scss 
  mat-color($button-primary, contrast(900));
  </code></pre>
  
  <p>See on the bottom it says contrast.</p>
  
  <pre><code>scss
  $mat-red: (
    50: #ffebee,
    100: #ffcdd2,
    200: #ef9a9a,
    300: #e57373,
    400: #ef5350,
    500: #f44336,
    600: #e53935,
    700: #d32f2f,
    800: #c62828,
    900: #b71c1c,
    A100: #ff8a80,
    A200: #ff5252,
    A400: #ff1744,
    A700: #d50000,
    contrast: (
      50: $black-87-opacity,
      100: $black-87-opacity,
      200: $black-87-opacity,
      300: $black-87-opacity,
      400: $black-87-opacity,
      500: white,
      600: white,
      700: white,
      800: $white-87-opacity,
      900: $white-87-opacity,
      A100: $black-87-opacity,
      A200: white,
      A400: white,
      A700: white,
    )
  );
  </code></pre>
  
  <p>How can I use the contrast?</p>