Okay this works, just adding “capability” (https://codex.wordpress.org/Roles_and_Capabilities) to the sub-pages.
acf_add_options_sub_page(array(
'page_title' => 'Colors',
'menu_title' => 'Colors',
'parent_slug' => 'theme-general-settings',
'capability' => 'manage_options',
));
Aaah, and 'position' => 2,
works, too 🙂