I have been to a couple of their events and I have never seen a participant who was obviously not Caucasian.
Which is ironic because the "open borders" movement really only exists amongst Libertarians. I'm aware that there is a strong xenophobic movement in Tea Party / Lib folks.
I'm in AZ, by the way. Home of SB1070.
Open borders is also a movement among international socialsts.
A response essay written by Eliezer Yudkowsky posted at Cato Unbound for the issue Brain, Belief, and Politics:
Is That Your True Rejection? by Eliezer Yudkowsky
The lead essay has been written by Michael Shermer:
Liberty and Science by Michael Shermer