In the system, using the CSS code, you can change the color of the main table header to green, for example. In order to change to it, go to the Settings> Account settings> Print settings tab, and then at the bottom of the page fill in the field Customize print with CSS  with the CSS code shown below:

}
@media all{
table.main_inv_table th {
background-color: #a0bf7f;
border: 1px solid #e1ead7;
}

 The example below is based on the Default template, but the above code works in all print templates.