...makes me laugh...by all means 'Pimp' a decent or even antique weapon, but AR-15's and Colt 1911-A1's...???
Having said that, Colt 1911's are popular amongst a 'certain' set due to the intimidation-factor - a half-inch wide muzzle in your face usually gets the attention it deserves...
The most pimping any of my weapons got were some custom wood-grips for my Browning Hi-Power that I bought back in the '80's and transplanted to each of my issued pistols in turn... now sadly redundant (along with my custom holsters) as we've gone over to the Sig-Sauer P226 instead...