The best example, cars, only goes back to 1990. And the museum objects are objects a science museum happened to keep, that go back to 1800? Hardly representative of consumer objects in general. There isn't even a single chart about clothing.
Glancing through historical clothing and car magazines from the past century is going to tell you a lot more.
The data shows an explosion of "new" colours in the 1960s, although the trend never stopped. Technology is still no doubt the answer – including the explosion in the black to white spectrum. We aren't limited to natural colours or colours, period, like we once were.
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.
I don't think it's really a meaningful visualization. They're trying to show something 2D in 1 dimension.
Also, pop art.
What happened was a lot of muted colors, earthy yellows, browns, and oranges in the 70s followed by an insane amount of the brightest colors possible in the late 80s and early 90s where fluorescent blues greens and pinks were everywhere. It seems like everything got a lot more bland after that and we've never recovered to happy medium.
I should mention that the Bauhaus (1920s)broke out color theory as separate from graphics representation.
Based purely on intuition, I want to agree with you. However, the data in the article suggests there's been a fairly consistent decrease in color of media since the 1800s. You would expect an explosion of color in the 1960s and then a decrease, but one does not exist. At least, the "explosion" the data shows is a very minor increase that does not affect the overall pattern.