parseColors = function (theme) {
            if (typeof theme !== 'string') {
              theme = '';
            }

            if (!attrs.mdColors) {
              attrs.mdColors = '{}';
            }

            /**
             * Json.parse() does not work because the keys are not quoted;
             * use $parse to convert to a hash map
             */
            var colors = $parse(attrs.mdColors)(scope);

            /**
             * If mdTheme is defined higher up the DOM tree,
             * we add mdTheme's theme to the colors which don't specify a theme.
             *
             * @example
             * <hljs lang="html">
             *   <div md-theme="myTheme">
             *     <div md-colors="{background: 'primary-600'}">
             *       <span md-colors="{background: 'mySecondTheme-accent-200'}">Color demo</span>
             *     </div>
             *   </div>
             * </hljs>
             *
             * 'primary-600' will be changed to 'myTheme-primary-600',
             * but 'mySecondTheme-accent-200' will not be changed since it has a theme defined.
             */
            if (mdThemeController) {
              Object.keys(colors).forEach(function (prop) {
                var color = colors[prop];
                if (!$mdColors.hasTheme(color)) {
                  colors[prop] = (theme || mdThemeController.$mdTheme) + '-' + color;
                }
              });
            }

            cleanElement(colors);

            return colors;
          }
@param {string=} theme
@return {Object} colors found in the specified theme