I could see an alternative design approach that beats Apple's focused on simplicity and ergonomics. Even all black and white only.

When I look at something, I don't want to be distracted by the things that might linger underneath, I'd like the system to support my attempt to focus.

I switched on transparency on my GF's (KDE) computer and for the first time she started to understand the concept of multi tasking.
Before she would shut down whatever she was doing before starting up something else.