Hey Tom, got two minor problems here:
1. gp-premium/colors/functions/functions.php
'title' => __( 'Back to Top Button','generate-woocommerce' ),
should be 'title' => __( 'Back to Top Button','generate-colors' ),
instead.
2. In Customizer -> Colors -> Header, if you change the color in ‘Link Hover’ and then hover your mouse over the Site Title on the right, you’ll see that it incorrectly renders this color in the Previewer (this shouldn’t have effect over the site title, as you can see by saving the page and try to view it again). Seems to me this option is using postMessage transport and it might not get handled carefully enough there on the client-side scripts.