From memory. Talk about change. It was the Conoco-Pennzoil joint venture and the start of the new Group 2 base stocks in Lake Charles, LA circa 1995. Removing all the "junk" from the nasty crude left the refined oil looking like ice water from Denny's. Conoco called their new oil Hydroclear and Pennzoil Purebase. Adding additive packages gave the motor oil color. Pennzoil darker with it's exclusive additive package with Z7.
Mobil around 1995 was first with a liter bottle but contained 946 mL of oil. Conoco was last to shift to the newer liter bottle circa 2002.
I used to hang around a lot of refineries. What an education!