Starting v1.17, custom colors no longer have option to use custom colors YES/NO. If you have colors set in Design settings, they will automatically show on the site after update to 1.17. When you update the theme, edit colors and delete / leave blank the custom color fields to have the theme default colors.
Colors available in this area are showcased in below screenshots:
You can add simple custom CSS in the custom css fields available here. BUT, for more complex css modifications we recommend to install the child theme in the theme pack downloaded from Theme Forest and make the changes in there.
Other colors you can change in the theme, from other theme options: