I just thought I would broadcast here that this issue remains unchanged in SketchUp 2020.0.
Yeppppppp. (insert sigh here) I’m still eye dropping textures (colour sampling) between models.
BTW, here is the list of items (materials related) that were fixed in S.U. 2020…
(Mac) Fixed an issue where adding transparent material with the Paint Tool duplicated material.
(Mac) Fixed an issue where painting with a duplicated material incorrectly applied the original material.
(Mac) Fixed an issue where Materials → Selecting a color did not set the material as active.
(Mac) Fixed an issue where copy/paste duplicated materials.
However, I would have thought the issue raised in this post would have at least trumped the final two ‘fixed’ items in the list.