I don't get it either. I open the Finder app, and the sidebar is randomly turquoise, over a white background.

It looks ugly, and I have no reason why that sidebar (unlike all other sidebars) is that specific colour. It just makes no sense.

Edit: Oh My God. I just tested installing my own app on Tahoe, and the DMG looks absolutely broken with what used to be solid edges confined inside a window, now being stretched to the window-edges, blurred by the glass-effect making the header on top unreadable.

THANKS APPLE. Jeez.