How to change the header background color of the group box

Experts,       In my project I have included a groupbox in a collapsed mode. By default, the group box has a greyish background color on the header (where we put the caption), as shown below:      Is it possible to change the grey color to something else? If so, how to do it. I tried to set the background color in the Style option, but that did not help as it sets up the background color for the entire group box. I am looking for the color change on the header section.    
1 answers

Group boxes can be styled with the default classes described here:

Or you create your own classes like the default,  with different color