squeeze the net hard enough, you get lemons.

consider the color negative. That piece of orange film -- so it seems. The base must be orange. It isn't. The orange is within the emulsion. Its purpose is color correction of dyes used in the Color Negative-Positive process of image making. 
I used to demonstrate, and have students attempt to duplicate with their explanation the following "test" -- experience.

     We will process color negative stubs (short 12 exposure rolls)
-- One is processed in D-76 developer  -thru fix, wash, dry. It may contain images. Your choice.
-- Another isn't exposed, it is unexposed but processed fully in Color negative line (C-4!) -- thru all chems, then dried.
-- Final one isn't exposed, but it isn't sent thru any developer. It is only fixed out using the C-41 fixer, then washed and dried.

Question: what are the differences? firstly, what do they look like? And, what are the differences in their curve shapes? Why do you think that is.

In this day, 2026, the mask is considered by most as existing uniformly and present in the "base". 
Adding a test -- can the orange be removed from the film: 
-- using abrasion
-- using chemistry

Did the base of the film disappear, dissolve, or merely look more like BW clear base.