Jerry,

Barra and Colonsay are two differnet islands. But as far as I know (and I don't claim to be an expert on MacNeil history) the MacNeil of Bara is the chief of the clan, and the senior line. So I would say that unless you knew specifically that your family was from the Colonsay MacNeils, the MacNeil of Bara tartan would be appropriate to wear, since your clan cheif is on Bara.

Aye,
Matt