Either you're very young, or have some agenda. Scroll down to the Windows section here and observe all the customisation we have lost over the years:
https://guidebookgallery.org/screenshots/appearance
In particular, look at this:
https://guidebookgallery.org/pics/gui/settings/appearance/wi...
Windows 1.01 already let you change the colours of almost every UI element.
A computer is part of the room. It's part of the furniture. It's part of the looks. I should be able to decorate the digital desktop, as much as I am able to decorate the surrounding desk and room.
That sounds a bit weird: Up to and including Windows 7, you could pretty completely customise the look of your system just using the built-in control panel.
I don't mean you chose colors and corner radius because you want to make your buttons look like candy. I mean features like text sizes and high contrast , go check your iPhone Accessibility section (but only if too many settings won't affect negatively, there are probably many options and labels to read).
My point is that hard-coding fonts,sizes and colors in your app is against accessibility, some fonts are harder to read then others for some people, small sizes is obvious the issue, some people need higher contrast then gray on white to read comfortably. If you are a competent dev or designer you need to understand that your app needs to work if the user wants a different font and different colors, Apple has guidelines. What would be nice is to think about the app as a tool that lets the user do a job and not like a work of art that a desgner needs to add it to a CV,
Yeah, and that sucks. Why the fuck don't they? Until fairly recently, "the" proprietary OS -- Windows -- did offer different colours for everything, not just some accent colours. Taking that away (with the introduction of Windows 8) was a humongous dick move.
What makes you think that (previously most, and now all) proprietary OS vendors perpetrating this humongous dick move is somehow an argument in its favour?
In fact, no proprietary OS offers different colors other than some accent colors.
Which Gnome developers have already said they will bring in future releases.
Heck, they aren’t even against theming. They are taking a wait and see approach to see if they can include more theme customizations without causing remarkably more work for app developers.
In fact, they are absolutely fine with developers who want to provide additional themes doing so. To the point that Gnome developers have themselves added additional theming options to default apps that will be released in Gnome42.