How do I apply "Blending modes" to UI objects?

I’d like to achieve something like this:

http://i.imgur.com/Ma44lvl.png

The black info box would multiply with everything underneath so its nice and readable, and be semi transparent. Just like “multiply” in photoshop.
Fairly straightforward I think, just haven’t done anything like it, a nudge in the right direction would be awesome! Search has come up empty because I’m not sure what terms to search.