This'll surely open up the whole "5.56 is/is not the same as .223" argument. But, regardless of opinion, you have a rifle with a 5.56 NATO chamber which will shoot all military 5.56 ammo as well as all commercial .223. It doesn't matter what the receiver is marked. Should be a great shooter. The commercial Colt's are good guns and you got a deal on this one it sounds like. Can you post a picture because Colt's website doesn't list model names, just numbers (all their commercial rifles are "Match Targets")?
FYI, there are two divisions to Colt firearms; Colt Defense and Colt Manufacturing. Colt Manufacturing markets for the civilian shooter while Colt Defense markets for the LE and Military. Your rifle comes from Colt Manufacturing, but that's more about marketing than about quality. . . they're both about the same.