Initially photographers were also the darkroom workers developing their films and fabricating the finished prints. As the camera became more manageable, laypeople became photographers. These amateur photographers entrusted developing and printing to photofinishers. These became highly mechanized shops common in every metropolis. These shops eventually processed black & white and color films.

Then came the one-hour shop that processed and printed in the neighborhood. The cost to equip a one-hour shop was high and likely floor space limited so these shops specialized to just handle color negative film leaving black & white and slide film to the wholesale photofinishers.

In an effort to expand the business of these one-hour shops, black & white films developable in color negative film processes were devised. Like their color film counterparts, these films contain dyes that blossom and become full blown in the color negative developing machine.

In other words, the small one-hour shop only capable of color negative film developing and printing, could now offer black & white service if the photographer used this special film type.

Let me add, ordinary black & white films are not compatible with the chemistry of color film developing and XP2 and is not compatible with the chemistry of the black & white process.