You can powdercoat the back and the faces but not the actual belt surface.
Even colored anodizing wears off fairly quickly. Only the hard anodizing last on the belt surfaces. That's what Metco uses on their belt surfaces. It's the shiny gray coating.
And if you do decide to go with powdercoating make sure the coater knows to not let any powder get into the area the bearing gets pressed into.
Ron...I looked into this a few years ago, I wanted some torch red pullies for my car
I ultimately decided against it for what was mentioned above. Over time the surface the belt touches will wear away and look crappy.
I talked to Midnight Powder coating near you, he recommended I stay away and stick with the anodized coating that Metco offers. I ended up with the black pullies and am very happy.