If this a one off frame custom built by Colnago for a customer, then it must have been specced without any of the identifying features of a Colnago frame except possibly for the head lugs cut outs and even those look a bit different from the ones I've seen!
Some unusual points:
internal routing with protruding tube,
square cutouts under bb
no "Colnago" engravings,
no tubing sticker,
"Columbus" droputs rather than "Colnago",
fluted seat stay caps, which are not one of the styles on late 80s frames and also look different to the ones on early 80s frames,
paint on the stays are unusual as already mentioned.