"White paper is cheap"
White paper is more expensive to create. It needs a bleach process, especially paper made from wood pulp, where many components would give it a brownish tint. Also, any amount of lignin left in the process will make it brownish with time (like newspapers, which use a low-quality, cheap paper).
I don't remember if "rag" paper (made from cotton and the like) is whiter without much additional processing. Some photo papers add OBA agents to make the paper look whiter.
Don't know about inks, but I'm not sure black inks are cheaper than other colors, especially in the past.
Also, reading dark papers in darker conditions is worse than white ones, because far less light is reflected and that mean your eyes may switch to low light, low resolution receptors....
Biting the hand that feeds IT
