The reason for non-band marked cable pairs has to do with a few things. First, polyethylene insulation really can't have another color applied to it. It won't stick. Second, the reason they use polyethylene insulation is that it can be much thinner than traditional PVC, which helps to reduce the overall diameter of the cable. By this same logic, believe it or not, the thickness of the colored stripes or bands will actually increase the diameter of the cable as well when you're talking about hundreds of pairs. It's all about keeping the cable as small as possible to reduce weight, labor costs and most importantly, maintaining a maximum outside diameter of 3.75" so that it can be pulled into 4" ducts.

Ed Vaughn, MBSWWYPBX