Hi Todd,
Unless you are lubing the tubes, the closest grease to the area would be from the u-joints. Check for a leaking u-joint boot. Another long shot would be a pedal cylinder on that side squirting or misting some fluid as you use the brakes. Check for any wetness at the pedal cylinders, hoses, etc. If it's a dry blackness, it may just be "smoke" from metallic erosion of the tubes. The OEM collars may have a glass fill, we are not sure yet.
Jim
Jim that's what it is-a "dry Blackness", it's not wet.