Remove post category gray box overlay

First off, thank you for such an awesome theme! Really appreciate your work.

Can someone help guide me on how do I remove the gray box that contains post category text? It’s the box that’s overlaying featured image thumbnail. Please excuse my description and take a look at the picture (in my case, it’s the ‘promotion’ tag): https://dl.dropboxusercontent.com/u/9895418/expound.jpg

Or my website: http://banmoh.net/promotion/

Thank you again!
Pete