ASTM A6 is: "Standard Specification for General Requirements for Rolled Structural Steel Bars, Plates, Shapes and Sheet Piling". The Scope states: " This specification covers a group of common requirements, that unless otherwise specified in a material specification, apply to rolled steel plates, shapes, sheet piling, and bars under each of the following specifications issued by ASTM: ..." Listed are the most common materials used in structural applications, including A36.
I said all that to say this; your column is not an ASTM A6 column. Chances are you will not have a problem because chances are the column's material will be found on the list. Chances are if it is a reasonably new building, it will be either ASTM A572 or A992. Somewhat older buildings may be ASTM A36 (which is what I am guessing since you stated the beam is A36). Just find out what the column material really is and you will have the first part of your problem solved.
As for weld compatability, there will need to be more information given about the weld that was deposited.
thcqci offers some good info for you. It is true that ASTM A6 is a specification that governs the quality, documentation requirements, ordering practices and etc for most structural steels. It has nothing to do with the actual material designation.
If I had to guess, I would say that the draftsman left out the "3" when ASTM A36 was intended.
Chet Guilford