I can understand the reasoning, but I would have weighed the significant benefit over the little "complexity"/content increase.
The color inversion is a significant effect. It doesn't change anything for those that use their own error pages, but significantly improves the situation for people who land on these pages and are bothered by light mode.
Waaaait - I recently implemented a simple dark mode for a simple page and thought color-scheme declares intent/support not influence how it is being rendered. I thought I still had to define dark coloring.
I just checked and to my surprise the browser indeed serves different default/root coloring when dark color scheme is declared [as well]. :O This means I can simplify my CSS.
I must have been misled when skimming by "specifies compatibility" and "Component authors must use the prefers-color-scheme media feature to support the color schemes on the rest of the elements." missing the browser behavior change description.
Seems like a very simple, lightweight and elegant solution to keeping the engine up to modern standards. If they were serious about keeping complexity out they wouldn’t have such garbage site configuration.