It's always been my understanding that the CC engines came painted Federal Yellow from Kohler starting with the Original through 1X8/9 series. For most of the 60's the SG was also installed by Kohler and was painted yellow including the SG belt as the engines were painted nearly complete at end of Kohler's production line.
I recall setting up new Cub Cadets in the late 60's and the SG belts often had yellow paint on them. Somewhere during late production of 1X6/7 series, IH started procuring and installing the SG's and belt at the Louisville works as the SG color was black instead and the belt no longer had paint on it.
Pictures have been posted on here in the past showing paint operations at the Louisville Works where the frame, transmission and steering box are assembled to the frame and are hanging vertically from an overhead rail while being painted. Once painted the frame/transmission then moved to the final assembly line where the steering tower and engine were integrated to the frame. All piece parts (grill, fenders, seat brackets, sheet metal etc.) came to the line already painted at this point. I expect the only painting that likely occurred on the final assembly line point was for touchup purposes only.