Alright, let me clear this up. The two gold ones belong to SonAir and are flown by Atlas crews in an CMI contract, IAH to LAD and back, three times a week.
The one blue one with N194UA on it, is an United plane leased to Atlas to get into the AMC pax business. It will be returned at the end of the year, unless they end up extending the lease. THERE ARE NO plans to convert this plane on Atlas's part. It is an old P&W powered plane, not the type Atlas is interested in.
I do not know what the forth plane was. We have had some cargo charters going into IAH lately, may be the other bird you saw in Atlas colors.
The United plane will be replaced with a JAL -400 that is in HKG for conversion to AMC seating arrangement. Rumor has it that there is a second JAL -400 that will be joining the Atlas fleet in early 2012.
These have nothing to do with the 767's. They will be doing their own flying with AMC.