Magnetic Shields

[HummerNewbie]

I am looking into buying a roll of the magnetic material they use for signs on vehicles. I have found a great deal on a roll that should more than cover every place I want to but have a few questions.

First, I can only find this material with a white face. Has anyone ever found any that is black on both sides? If is comes down to it, could I paint the white or something like that and would it stay on this flexible material.

Second, what mil thickness should I go with. Basically I am looking to protect against scratches from brush and branches. I am not going to go where I have something thick rubbing down the side of the vehicle so I would think the magnetic material doesn't have to be that thick.

Any input would be appreciated.