The red is the color of the PRI party in Mexico, the old party that ruled and ruined Mexico for 70 years. They are socialists, but not really ideologues - you occasionally find good people among them. They're just a great big amorphous party and down in Oaxaca, they were apparently defending their privileges against people to the farther left of them, like the Indymedia guy. Neither the PRI, nor the PRD nor the Zapatistas they were fighting are connected with the current party, PAN that is in power. The people they were fighting were all from the left and the far left. It was dinosaur left versus chavista left in this battle, left on left violence.
Which is probably why the msm is not interested in covering this.
Thank you for that explanation! It is much clearer to me now, and, yes, I think you're right - the MSM would never want to cover what is essentially a violent power struggle among leftists.