Asingle color can appear to change hue, value, or saturation because of

a. linear perspective
b. relative edge
c. median transparency
d. color vision

I think its either A or d maybe C sorry if its not helpful

photography had emerged as an elite art pursued by a few creative individuals for a few wealthy patrons. but now, said bauldelaire, it was succumbing to "the great industrial madness of our times." it was becoming a mass production industry that catered to middle-class tastes, including a taste for gadgetry. the stereoscope, the first 3d imaging system, had turned looking at photographs into parlor entertainment. a "thousand hungry eyes were bending over the peepholes of the stereoscope as though they were the attic-windows of the infinite.