To change the color of the WooCommerce alert, you just need to add a small snippet of CSS code under Divi > Theme Options in the Custom CSS section.

The only thing you replace here is #eb4034 with the hex code of the color you'd like to use. In this example, we wanted it red so we chose #eb4034.

.woocommerce-store-notice{
  background-color: #eb4034 !important;
}