get rid of the grey part in the slider

Hello,
I am using the Mystile theme for my web site and on the slider I want to get rid of the grey part where the title and the excerpt appear. (even when I clear all the text the grey part stays, I also tried to download a plugin but it is not doing much…).
I am not so good at coding so I was hoping one of you could help me with some accessible directions.

Thank you very much

As