code: function transformColor(string) {
    return parser(string).walk(function(node) {
      if (node.type !== "function" || node.value !== "color") {
        return
      }
  
      node.value = colorFn.convert(parser.stringify(node))
      node.type = "word"
    }).toString()
  }
docs: Transform color() to rgb()
  
  @param  {String} string declaration value
  @return {String}        converted declaration value to rgba()