I just remembered I made a silver key model so you can actually change the color in the object editor, it looked horrible... But here is a new version I have made today!
No custom textures were used in this one. Just give credit if you use it in your map
There are actually two forms of making the 4 keys, one is changing the color in the object editor and another is changing the texture in the mdl, since it uses the moon key icon as texture you can use the other 3 key icons for this.