I know this one! Y'know that artist who has all those paintings with the Blue Dog in 'em? Can't think of his name right now, but Rodriguez rings a bell. Well, anyway, a bunch of southern Democrats wanted to organize as a more conservative wing of the party, and they regularly met in the offices of some congressmen who had these paintings on their walls.
A friend of mine's into that guy's paintings... I'd wondered if there was some connection.
I figured it was just a new twist on the old "yellow dog Democrat" thing. I'm not sure where "yellow dog" came from, but I know quite a few older Southerners who claim to be "yellow dog Democrats." I think it just means "die hard" or somethin'.
Ah - wanna know somethin', do a Yahoo search - link.
Basically, a self-professed Yellow Dog Democrat would prefer to vote for a yellow dog than vote for a Republican candidate.
Hmm... that gives a different explanation for Blue Dog -
In 1995, a group of Democrats in the House of Representatives began calling themselves Blue Dog Democrats to indicate that they had been choked blue by the dominance of liberals in the Democratic Party.
...but that doesn't discount the painter story.