By sampling pixels from movie posters since 1914, Vijay Pandurangan has compiled a bar chart showing how the distribution of basic hues has shifted over the years. He ignored black and white, and also cancelled variations in value and saturation, showing the colors in their purest form.
Can we draw any conclusions about changes in the zeitgeist? Here's one suggestion: there seems to be a slight increase in cool colors after the end of major U.S. wars. Notice how the blue spikes for a year or two following 1918, 1945, and 1975.