[sphere and ash]

I think there are three possibilities:

(i) Different color stamps were used in different years.
(ii) Different color stamps were used at different manufacturing facilities during the same year.
(iii) Different color stamps were used at the same manufacturing facility during the same year. (This, for me, is the most likely reason. I have seen major, branded American manufacturing companies use inconsistent colors in their logos just because a plant manager is not thinking about it. In Spalding's case, this is just a stamp on the side of a ball, and it will be largely rubbed off after a few minutes of play. It might not have been given a second thought.)