F.Y.I., the UI logo on the front of the mag is Universal Industries. They were the subcontractor back in the day that manufactured the 20rd mags for Colt. I bought an AR15 (SP1) new in the box in 1972. It came with (2) 20rd mags, blocked to 5rds. These mags came from Colt with Universal Industries marked floorplates. I still have them. Apparently, at that time, all Colt marked floorplates were going to the military.

That is an awesome looking pair of Colts you have there. I especially like the US Property marking. What does the paperwork consist of there and how long does it usually take to go through the process?

By the way the coloration of the barrel is due to bare metal subjected to high heat. The metal tends to oxidize somewhat during the cooling of the barrel. Totally normal and adds to the overall character of the rifle. Well done!