Javascript String colorHex()

var reg = /^#([0-9a-fA-f]{3}|[0-9a-fA-f]{6})$/;
String.prototype.colorHex = function(){
 var that = this;
 if(/^(rgb|RGB)/.test(that)){
  var aColor = that.replace(/(?:\(|\)|rgb|RGB)*/g,"").split(",");
  var strHex = "#";
  for(var i=0; i<aColor.length; i++){
   var hex = Number(aColor[i]).toString(16);
   if(hex === "0"){
    hex += hex; //from w w w  .j  a  v a 2  s  .  c  om
   }
   strHex += hex;
  }
  if(strHex.length !== 7){
   strHex = that; 
  }
  return strHex;
 }else if(reg.test(that)){
  var aNum = that.replace(/#/,"").split("");
  if(aNum.length === 6){
   return that; 
  }else if(aNum.length === 3){
   var numHex = "#";
   for(var i=0; i<aNum.length; i+=1){
    numHex += (aNum[i]+aNum[i]);
   }
   return numHex;
  }
 }else{
  return that; 
 }
};