This is a custom CSS element and will need to be changed within the stylesheet itself via Appearance > Editor > style.css. Just look for the class “.anthemBlurbColumn” and its proceeding entries to change the background-color values.
.anthemBlurbColumn1:hover {
background-color: #378fea;
}
.anthemBlurbColumn2:hover {
background-color: #4528bb;
}
.anthemBlurbColumn3:hover {
background-color: #de2e4c;
}