@ cube --- As to your question -- How optical color darkroom practices deal with the Evans Integral Orange Mask?
The C-41 color negative film process utilizes dyes incorporated in the film during manufacture. There are three, cyan (blue + green), magenta (red + blue) and yellow. The dyes in the film are incomplete. During the developing process, a black & white image forms each emulsion layers. The developer also contains a single missing dye ingredient that will unite with the incomplete dye. This action occurs as the black & white image is forming. This action causes the dyes to blossom in proportion to the black & white image. The process then removes the black & white image. The result is a color negative image consisting of dyes.
The predecessor Kodachrome process required three discreet developing solutions. Think about how difficult it is to make cyan, magenta and yellow dyes that are all missing one single ingredient. Some compromises must be made as to the colors of dyes. As it is, the cyan dye is far from perfect, the magenta dye is fair, and the yellow dye is quite decent.
Prints made from these negatives were yielding substandard results. This problem was solved by Ralph Evans of the Eastman Kodak Co. He tested and found cyan and magenta dyes what in their un-blossomed state have a tint. This tint wanes as the dyes blossom. The orange you see is not a uniform tint. It is strong in areas that were not deeply exposed in the camera and weak where exposure is hefty. In other words, residual cyan and magenta dye form two positive images superimposed atop the three negative dye images. The residual tints appear orange. This is the Integral Mask; it is a countermeasure for the inequalities of the cyan and magenta dye that must be used.
Color negative films are intended to be used to make color prints by optically projecting the color negative’s image onto light sensitive color paper. These papers have three emulsion layers, each has a different paper speed (ISO if you will). Thus the printing paper is tailor made to cancel a color cast imposed by the orange mask.
Think about the complexity, of the predecessor, the Kodachrome process. This process usually had on duty a chemist and quality control engineer. To simplify a single developer step was needed; Thus the C-41 and the E-6 process both use this same scheme of a single missing ingredient in a single developing solution. No color film yet made produces a faithful image. Nevertheless, the E-6 and the C-41process makes excellent images.