I have a Nexus 5 and I recently installed Android 5.0 (Lollipop).
The task switcher in Lollipop makes is much easier to see the screen contents of each background app as you are switching between them.
I notice that my banking app shows the contents of the screen in black when switching to it - an obvious security measure as you don't want people viewing your banking details.
Is there a way to apply this security measure in a more general fashion to any app? An obvious workaround is to close the app each time you exit, but this is a bit annoying.