What Color are Libertarians?

In the comments on a prior post jamesk suggest blue states and red states could pair off to do proportional representation of U.S. Representatives. It's a lovely idea, and wholly constitutionally acceptable. But, I noted, the blues and reds won't do it because it would help the greens. And, I added, "the libertarians, whatever color they are."

Libertarians ought to be green, perhaps, the color of money, but that's already taken. So here's my new poll: what color should the libertarians be?