Given Time is an excellent post. Especially his explanation for the transparency stands out.
Where keyboards, pickers, and action sheets were once imposing screen elements with a lot of personality of their own, they now reflect the personality of their environment. Your bright red app won’t have a dull blue-gray keyboard anymore; it’ll have a light red keyboard as the bits of UI beneath it shine through. If your app uses a lot of wood textures, the standard action sheets won’t look out of character because they’re no longer plastic. No matter what you do with your apps, iOS 7’s default visual language will be a better complement.
Never had thought about the transparency of iOS 7 in this context. Please do read the entire post for some exciting insights.
via (Stephen Hackett)