What made it white in the early missions was paint, which weighed (IIRC) a couple of thousand pounds. They stopped painting the tanks to increase payload capacity. The insulation itself has always been that orange/brown color. Painting the tanks wouldn't prevent foam from breaking off.
It's a paint/sealant. Preventing water from getting into the foam and freezing couldn't hurt.
Ice will damage a frickin' road bed, it can't be any good for foam!