If you look closely, there's actually an increase of red, green, blue, etc. at the same time as the increase in black and white, and it's the brownish colors of undyed organic materials that are decreasing. (Or maybe they were originally dyed and the color faded over the last 200 years.)

Whereas before you might've been limited to a choice of lighter or darker wood for your furniture, now you can have it in any synthetic color you want, including pure black and pure white.