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It would be nice if the phosphor reflectance could be made dark independent of its light-emitting properties, but that's just not the case. CRT faceplates have always used a neutral tint if any in order to improve the contrast (except for the very earliest experimental tubes, some of which needed filters to help get a decent red and suppress the much more efficient blue and green). Some modern tubes use a different colored pigment on each phosphor to reduce its reflectance while letting its primary color through.
One possibility, which I have not heard mentioned, is that when going from NTSC phosphors to sulfides, a darker faceplate was used - so a slightly greenish appearance just became darker. The 1973 paper also says that the green phosphor went from silver-acivated zinc-cadmium sulfide to copper-activated zinc sulfide in 1968, which had "a more nearly white body color". However, I think I recall that Zenith-Rauland was using cadmium up until the 1970s. Manufacturers eventually eliminated cadmium because of environmental restrictions.
Regarding black matrix tubes, this was one of the big inventions fo the mid-70's. All tubes use the black matrix technique today to reduce the screen reflectivity. Along with this came the concept of "negative guard band" for better purity.
The early tubes had positive guard band - that is, the holes in the shadow mask were smaller than the phosphor dots. If the beams didn't approach the screen at quite the right angle, there was still some room for them to be off center and still hit the right phosphor dot. However, this could lead to white-field impurity if the dots were not uniformly efficient. When black matrix was added, someone got the idea of making the holes in the black matrix smaller and the holes in the shadow mask bigger. Thus, the electrons hit all of the dot and some of the surrounding black matrix, and their aim can be off more without causing part of the dot to be unlit or wandering onto the wrong color dot. This makes the purity adjustment have a larger tolerance - purity tends to stay good up to the limit of misadjustment and turns bad more suddenly at the extreme.
Combining negative guardband with in-line guns that don't care about vertical displacement of the angle, allowed the introduction of self-converging deflection yoke/tube systems that did away with all the convergence circuits and need for setup in the home. This was a big part of keeping the price of a TV constant or falling in current dollars (and always falling compared to inflation).
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