Yes, it's a tubing made by Columbus and It's probably SL which is the grade of tubing the frame is constructed from.
A lot of 70's and early 80's high grade racing bikes were made from these tubes so it is no bad thing, In fact all my bikes bar 1 are Columbus SL.
The one you are looking at might be a Super Pui and you can check it against this one;http://saarf.net/category/colnago-super-pui/
In particular you want to look at where the skinny tubes at the back (seat stays) meet the bit where the saddle post goes in the frame and all the tubes meet (the seat post cluster) and compare the joint and the ends of the seat stays with those in the link above. If they are the same then you are a lot closer to identifying your Colnago.
Wether it's a good Colnago model I can't say.
What I can say is that as you are in the US you can get a lot of bang for your buck if you look hard enough.http://www.ebay.com/itm/De-Rosa-Profess ... 43be3b23a2
Damn!, thats a fine bike. Not sure about the seat though http://www.ebay.com/itm/1980s-vintage-1 ... 2a26013566
The Merckx might look like an old banger, but it's really a very good bike designed by Ugo De Rosa. Top quality although the price is a little steep and it needs a Super Record derailleur and some record SL pedals.
Mmmmmmmmmmm..... Nice Betty