I don't think I've ever heard either "Colours" or "When All Men Sing", in a folk club or elsewhere.

At a guess, the one song I've heard more often than any other in Scottish singarounds in the last few years is "The Road and the Miles to Dundee". "The Star of the Bar" next, maybe.

Of the others mentioned here, "Lowlands" and "Caledonia" get done fairly often. Honourable mentions to "Your Cheatin' Heart" and "Copperhead Road".