We didn’t have color comparison cards, but I don’t remember how we evaluated the oil, either. Given that McDonalds’ operations are really well-engineered, I’m certain it wasn’t just a subjective call. All of our oil was vegetable oil (not tallow, which some markets still had), but it was that solid, hydrogenated stuff.
Yeah, we had liquid veg oil but our fryers were engineered to use the solid block of shortening. It always confused newbies in the kitchen when we would first fire up the fryers for the day. The fryers would heat up very slowly until I think they hit about 180 degrees by which time the computer assumed any solid shortening would be melted. At that point, it put the spurs to it with an impressive WHUMPF of the main burner igniting.
I always wondered why fast-fried-food restaurants were so often found in the same block as auto parts stores like Kragen or Napa or O’Reilly or Auto Zone. It makes it so much more convenient for recycling all the used motor oil.