It's a cute article, but I don't think it holds up under scrutiny. I suspect it is much more a collection of unrelated reasons:
* Historical objects in museums are likely more colorful because we cared to preserve the most visually striking objects. Classic survivorship bias.
* Music has less dynamic range than in early recordings because producers were competing to be the loudest sounding song on the radio (see "loudness wars"). Those wars are actually over now and dynamic range has been increasing for about a decade.
* There is a whole lot going on behind trends in cinematographer color grading if you look into that world. But in the example here, I think it's largely that audiences expected "muted brown" as the color grade to send a "period film" signal. Witness also how every medieval or fantasy movie feels compelled to have all of the castle walls bare gray rock when they were in fact plastered and brightly colored. Likewise Roman architecture being alabaster white. Audiences wouldn't believe a Roman movie with painted statues or a fantasy film with colorful castle walls.
* Cars have muted colors because consumers moved towards a model where they sell cars every few years. When purchasing a car, they choose neutral colors to maximize resale value. Also, I think cars are simply much less a part of someone's social identity and status symbol and more of a utilitarian object than they they used to be. (Witness that when people buy expensive sports cars, those are more likely to be brightly colored.)
* Interior design trends come and go, but I think one of the drivers of gray walls was that it became a popular style for Airbnb rentals to avoid turning off potential renters. That led it to become associated with internationalism and modernity, and from there it sort of took off. Also, an increasing number of people are renting and are simply unable to paint their walls more interesting colors.