I actually checked with the Climate Control dept. of York International, was told that they do paint some of their compressors black.
The person I talked to didn't know why some were painted and some weren't, but that they were spray-painted in a booth, and not powder-coated.
As far as the quality of the paint results, that person couldn't elaborate.
York compressors are used in a variety of automotive models, and quite possibly are painted based on the requirements of the vehicle manufacturer. I know that some of the earlier Jeep models had black ones.
Hope that sheds some light on the subject.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car