If it's a steel frame a Colnago is unlikely to have anything other than an Italian BB which is a righthand thread each side. As mentioned, most cups have a size marked on them. However if there's nothing to be seen, the best action would be to remove the LH cup which will have a 'normal' right-hand thread (I've never saw a non-drive side cup with a LH thread, even when I was dealing with French and Swiss bikes, so it's anti-clockwise to unscrew), remove the bb cartridge and take a look to see if there's anything on it to denote the fitting. If the removed cup is 36mm diameter then it's Italian - anything smaller presents something of a problem as BSA and French/Swiss are so close you can't really tell unless you try to fit them in a frame with known thread sizes.