Our developers have confirmed that an issue was found in PI WebParts 2013 that may interfere with the ability to do this. A PLI/Work item has been created to fix the problem. In summary, the problem is that in SharePoint 2013 the default CSS file (COREV15.CSS) includes the UserCaption class and assigns it a background-color of “f1f1f1”. As a result, the background-color of the child table is displayed regardless of whether the container DIV class (ms-WPBody) is assigned a background-color or transparency setting.
As a workaround, edit the COREV15.CSS and remove the UserCaption class background-color attribute.
I hope this helps!
Thank you for your reply. I could fix the issue!