It's less of a support thing and more like 'nod' thing for reddit.  It's giving a nod to the most popular story on the site all weekend.

Green is the color of Mousavi's movement.

Despite the fact that he is the popular alternative to Ahmenidijad in Iran, he is still not someone we should be supporting here on Reddit.

Waving the colors of his movement as a sign of solidarity with the Iranian people is misguided. Find some other way to show your support.

He wouldn't have been allowed to run for President if he was really that big of a reformist.

I'm bothered by the green wearing reddit Alien