The chain on my new bike seems to self coat and generate a black film that finds it's way onto the cassette/gears. Indulge the nooooby ness here please. Is the black coloration from the crank set teeth, which are also black paint ? Metal oxide ? Or just road dust and lube film ? The front gears, the crankset teeth, the I-Tree in Marley-Speak, appear to be painted black. Why would they do this ? - Road Bike ridden about 200 miles to date on dry pavement only.
All of the above. Fine metal particles from the chain, cogs, and crankset combined with foreign material picked up from the road are all mixed in with the chain lube. Aluminum cranksets (non-painted) tend to produce more coloration than steel. If you ever get that chainwheel gunk on your clothes it is almost impossible to remove. I have a T-shirt that has had a chianwheel tattoo on it for several years despite dozens of washings. I think the aluminum particles are the major culprit in the semi-permanent marking of clothes. All other grease except chain residue will wash out of shop aprons/rags.