Isn't the whole point of flat design replacing the loud superfluousness of skeuomorphism's textures with equally jarring psychedelic colour schemes? That's how designers prove their worth, by adding more stuff, right?
I mean, where do you see the: "jarring psychedelic colour schemes"?
If anything the grant-parent brings up the example of the Control Center, which is the opposite of that, just a two-color subdued thing.
I don't like the background of CC myself, but I think that's actually because they're letting the hue of the homescreen icons below bleed through too much. It's "neat" but I think it's kinda visually gross :S