> after abandoning better solutions (user-defined system-wide color schemes) that had existed since the early '90s on every platform except the vaunted Mac

Even classic Mac OS (pre OS X) had thousands of third party themes via the very popular extension Kaleidoscope and later the built in Appearance Manager. Kaleidoscope schemes especially ran the gamut, with looks ranging from cloning other OSes to green on black “Hollywood hacker” to Star Trek LCARS to shiny chrome to a pair of blue jeans. A great number of those themes were dark.

The loss of user control over appearance like that is tragic.