Chromado translates as chrome plated, not the tubing name or manufacturer.
25CrMo4 is standard Chrome-Moly steel (AKA 4130 steel). Same generic alloy composition such as used in vintage columbus SL/SP/Cromor tubesets. Probably indicates a pretty low end bike for colnago with cost savings from using generic tube supplier or mixing tubes from various suppliers. External tube diameter is most likely 28.6mm (1-1/8") for a wall thickness of 1.0mm. Usually the seattube is only butted larger on the bottom end and the top has same thin diamater at middle of the tube. Might be that they used a tube butted on both ends so 1.0mm wall thickness where tube meets lug, about the same end deminsion as columbus SP tubeset uses.
Odd that it is 126mm dropouts, may indicate that it is even older or was slighlty damaged in shipping. I would really expect most any decent 90's bike to have 130mm width.