Seriously, having every window the same colour, whether in focus or not, is a Really Dumb Decision. When you have multiple monitors, it’s very difficult to quickly see which window has focus. With seven monitors it’s nearly impossible; the black-text-vs-grey-text is woefully inadequate. I know applications can now choose their own colour, but that doesn’t help. In fact, it probably makes it worse. With Windows 7 and 8 I could choose a colour which contrasted strongly to the inactive window colour.
Another useful feature bites the dust. And another reason I’m considering dumping Windows 10 and going back to 8.1.