One issue: the paints/pigments available in times past were not the full range we have today. Sometimes they had to make things somewhat ugly to both our and their taste because that is all they have available. They would still have done their best, but there are limits.

We are hampered even more today because blues and greens tend to be sourced from organic materials that decay quick, while reds and browns are from minerals that don't decay (but flake off). Even in the best preserved art that we have there is still likely significant differences between what we see and what they saw because of this color change.

This is absolutely not true at all. In physical painting you do not have a colour wheel were you pick colours to slap on. You can create a wash of colours and hues just with Zorn palette. We are taught to use fairly limited palette in oil painting even today, although you can in principle buy every known hue and slap it on - but that is not painting and that won’t produce anything worth the canvas it is painted on.

You don’t need to believe me. Look at Egyptian sculptures that have survived fairly well in the tombs. Or Greek and Roman paintings, some of which have survived quite well and shown in the original article. I spent 3,5h cgoing through the collections of The Archeological Museum of Napoli, and there’s plenty of them. They used muted earth tones like most skilled modern painters would.

This is true, but it wouldn't produce the sort of flat coloring in the reproductions. It would limit the color space but artists could still blend and fade those colors to create intermediate tones. This is demonstrated in some of the beautiful ancient murals which the article uses for comparison.

Another thing is they may have wanted to use newly available colors to show they had new colors -the novelty aspect. Kind of like when people learned to make aluminum it was sought as a luxury item —whereas now no one would think of aluminum as a luxury item.