I would say that is probally a service replacement engine. As Harry said, they were black from Kohler. We ahve a 149 that had a complete replacement engine put in in the early 80's and it is black. Came with everything but the S/G and the PTO Clutch. The original Kohler had a piston skirt break off the engine started to have a bit more noise but nothing worrisome. It was our snow removal machine. Wehen we changed the oil there was metal that came out of the pan. Continuing to run it, we over bored the cylinder to the point it would need sleeved. So we bought the service replacement and replaced the damaged one. This engine and tractor are both still in service, and what started yellow and white fever for me.....
Also, once IH started the Quietline series 1x00/1x50 tractors, the engine was black from the factory, and it believe it is that way to this day. My 2020 CC ZR has a black engine, and the lawn and garden tractor lines have a black engine......