function getThemeColor(expression) {
      var color = extractColorOptions(expression);

      return parseColor(color);
    }
@ngdoc method
@name $mdColors#getThemeColor

@description
Get a parsed RGBA color using a string representing the `theme-palette-hue-opacity` of the
desired color.

@param {string} expression color expression like `'red-A200-0.3'` or
 `'myTheme-primary-700-0.8'`. Theme, hue, and opacity are optional.
@returns {string} a CSS color value like `rgba(211, 47, 47, 0.8)`