How to change or remove background in banner

I would like to remove the grey background under the text in the rotating banner.
The images I am using are dark and the grey background is not needed.

I edited slideshow.css to attempt to remove the background, works a treat in ie but in firefox I cannot get rid of the background at all. Tried clearing caches etc but no luck. Also shows up stubbornly in chrome. A couple of times the background disappeared, only to come back a few seconds later???

Any suggestions as to what to edit to get rid of the background?

Many thanks