(a) Changing the primary colour past a certain threshold is not a solution, in my experience: there are backgrounds where the contrast is too low, no matter what you do.
I've been playing with such UIs for years, and they've never left my personal setup, because – while very pretty – they're not worth the hassle. However, Apple's implementation here is particularly bad. (I don't see why anyone takes these companies seriously any more.)
(a) Looking around me, I'm struggling to find a photo I could take that wouldn't trigger this "edge-case" – so it can't be that much of an edge-case.
(b) I'd expect them to patch this particular issue, now it's been widely-publicised, but Apple's pushed bigger defects to prod over the last few years (e.g. https://www.applevis.com/bugs/ios/when-editing-text-using-ha...). I'd be extremely surprised if this feature shipped in a properly usable state, especially given that their marketing shows that several fundamental design flaws are works-as-intended.