There's so much in this essay to unpack, it's all over the place -- more of an extended rant than any particularly cohesive argument. But one of the early points is "why is everything so gray instead of colorful?" Which is easy to answer -- when all your cars and buildings are super-colorful, they clash. They become garish and ugly and screaming for attention. Thank god we've moved to more neutral tones that actually…
The rational explanation why the majority of items are neutral tones/grey is because this maximizes the market. This can be seen on automobiles, where silver is the most common color because it’s easier to sell second hand, so manufacturers learned to optimize for this.
This has impacts on the industries surrounding as well. If I want a custom siding color, it's going to be more expensive. We're normalizing everything around the most widely palatable, so it's all fairly bland.