Need some help with understanding Extensions

hey so im trying to make an extension so convert a color to a hex value eg 00ff00 would = green

this is my Script using UnityEngine; using System.Collections;

 public static class HexConverter
 {
     public static void ColorToHex (this string hex, Color32 color)
     {
         hex = color.r.ToString("X2") + color.g.ToString("X2") + color.b.ToString("X2");
         Debug.Log(hex);
     }
 }

http://wiki.unity3d.com/index.php?title=HexConverter this is where im getting the converter

and to call this im using

 void Start ()
     {
         ColorCode.ColorToHex(ActualColor);
 
     }

ActualColor is a color 32 and Color code is a string

the problem im having is that Colorcode doesnt get changed to the colour code BUT in my extension Debug.Log(hex); puts out the correct infomation

Please help thanks ~Scott