One of the options is to add a header image instead of the blue color.  That is what we have done for our courses.  In most cases we simply use the same image as the thumbnail or player background image.

It’s found in the Course Properties

If you just want to change the color gradient to use a different color, you can use something like this:

.dcb-te-content-overview-header-wrapper {

    background-color: red !important;

}
 

Swap out “red” for any color you wish.  Here are lots of possibilities:

https://www.quackit.com/css/css_color_codes.cfm