Are all 1911 .45 magazines interchangeable and brand specific?
There is no such thing as a “colt 1911 gun magazine”. 1911 is a type of gun, and there are many different manufacturers of 1911s. So there are just as many different brands of magazines for 1911s as there are manufacturers of 1911s. There are dozens of different brands of magazines for 1911s, and almost all of them will work in any 1911. The only exception would be if the brand of the magazine was made specifically for a certain model or manufacturer of 1911, and those models or manufacturers were not interchangeable. But that’s not common. In general, any magazine that’s marketed as being for use in “1911 pistols” will work in any 1911 pistol.
Some popular brands of 1911 magazines are Wilson Combat, Chip McCormick, Mec-Gar (the OEM manufacturer for many different gun brands), and Checkmate. There are many others.