An easy way to customize any gun is to make it a different color. While there are several different options for accomplishing this, not all are practical for the home gunsmith. If you're only planning on doing this with one or two guns, then the purchasing a spray kit and paint plus the air compressor to run it, simply isn't very practical. However, if you plan on doing this on a regular basis, then it might be worth your expense to purchase this equipment, and it can be easily attained from websites like Brownells.
If you're looking to customize the color of your gun without purchasing all this equipment, then a good alternative for you is the DuraCoat EZ Finishing Kit, available from lauerweaponry.com. This kit comes with everything needed, plus your choice of one 4 ounce DuraCoat color all for only $49.99. This size can will typically cover 2-4 guns. With 195 standard colors, 16 tactical colors, and 7 electric colors, there's sure to be one to meet your needs. This system works off a can of propellant rather than needing an air compressor. The DuraCoat system is known to give excellent coverage with an easy application, while providing good looking coverage that will protect your gun from the elements.
Feel free to post pictures of your custom colored guns in the comments section.