I would put the landing gear struts of a bare metal Mig in an aluminum overspray myself, I have seen that on Mig-21s.
As for the above photo, you've got a real mixed bag there. The blue is very similar to what went on the undersides of MiG-21s that had camoflage on them, the fuselage is bare metal and the inside of the gear door looks almost certainly aluminum overspray and very fresh at that.
I'd say your probably looking at an aircraft that had camoflage at one point and was later stripped of paint with the exception of the gear and gear bays (perhaps they were retracted at the time of stripping) As for the gear door, likely just a new replacement part. That would explain its much fresher appearance in relation to the rest of the aircraft.
If you look at pictures of Soviet aircraft, you'll notice they aren't really babied that much and improvizing repairs in the field was not at all uncommon practice by Soviet maintenace crews. I suspect this aircraft had been around the block a few times when this photo was taken and it had been a while since it had seen real extensive maintenance. Probably late in its career I'd think, certainly not indicative of a new aircraft.