I don't think this can be written off as just change aversion. The lack of obviousness of which tab is currently selected is a real problem.
I'm a primarily UI-focused engineer with heavy involvement in UX, and this immediately struck me as problematic. You should not have to look at the tabs and think "Now which one of these colors/icons means 'currently selected'?" but with this UI design, if you have 2 tabs open, that is exactly what happens. With 3 or more you can kind of tell by which one is different than the others, but you still have to think about it for a split second. You shouldn't have to at all.
Additionally, consistency is a basic hallmark of good UI/UX, and by having the tabs and chroming "pick up" the colors of the page, it makes this process even less obvious. For example, let's say you get into the mindset of "the dark tab is the selected one". Is that always true? No, it is not. If you go to a dark page (try theverge.com for example) this rule is *reversed*. So that means you have to not only take a second to think it over, but evaluate whether it's true in the current color scheme!
This is a rookie UX mistake, and I am a big Apple fan and enthusiastic developer, but I am shocked that they did this. This is really beneath their usual UX competency. Honestly.
But hey, let's not be theoretical. Let's look at real examples! Here, I've opened just two sites: news.google.com and theverge.com, each in their own tab. The *only* thing I'm going to do differently in these two screenshots is change tabs. Nothing else.
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Okay, at a glance...what's selected? The dark one, right? So now let's change tabs:
View attachment 1856647
Quick, which one's selected?
Do you see the problem?