I think the tanks are identical. Both are high pressure tanks which contain compressed gas which does not liquify under pressure. I don't think either gas contaminates the other to make the tanks non-interchangeable, but I could be mistaken about that.
Argon is an inert gas, the third most common gas in our atmosphere despite existing in minute quantities, which is used as a shielding gas in its pure form in GTAW (TIG) welding, and mixed with CO2, and sometimes with small amounts of oxygen, as a shielding gas for GMAW (MIG) welding. A mixture of 75% argon, 25% CO2 is a joy to weld with in GMAW, much nicer than pure CO2.