I don't even think the increase in variants has much to do with the backlog. They may be pressing 10 different variants, but they're not pressing 10 times as many albums to just sit on shelves.
It has a little because coloured pressings take longer because they have to thoroughly clean the press between colours to stop contamination whereas that is not necessary between pressings with only black. But the real issue is sales and demand outstripping pressing capacity by a pretty large margin.