Recently, I bought a new and sealed 70828 Pop-up Party Bus, 2019, a quite underrated set, in my opinion. I was surprised to see that the many white parts are not as white as I expected. I compared this set with white elements from my other sets. On the picture, you see elements from the 5974 Galactic Enforcer, 2009, 70810 Metalbeard's Sea Cow, 2014, and the 31109 Pirate Ship, 2020.
It is not quite obvious on the image, but all sets have exactly the same, ivory white. For comparison, I placed them on a blank white paper. I remembered having seen much brighter shades of white in older sets, so I dug deeper and found a 6982 Explorien Starship, 1996 with many yellowed white parts, but also some parts that hadn't yellowed at all: On the picture, you see the famous 30037 Wing Plate Bi-level 12 x 9 x 2 1/3 over the Pirate Ship sails. Again, the light for the picture is not the best, but the white colour from 1996 is much brighter than the more recent version of LEGO White. I assume that in 1996, all white parts were of the same hue.
My question is whether there was a change in the LEGO colour "White" and whether this change can be attributed to a certain date or a known change in the production process?
Any hint is appreciated. Happy new year, by the way!