The red overlays usually linger long enough for me to hover/click and find out more, but whenever I see the black overlay, it always disappears before I get the chance to see what it's trying to tell me. I did manage to capture this screenshot, which in this case is a Flex Repeater containing eight embedded checkbox views.
The red overlays can be repressed with "Overlay Opt-Out", but as far as I can tell, these overlays can't.