[beta7] Theme settings does not support sub-theme

Problem/Motivation

If UI Suite DSFR is not the default theme, the settings available colors is not working.

theme_get_setting usage should be contextual to the theme which settings are changed. The second parameter specifying the theme should be used otherwise it is the current theme that will be used, so the admin theme.

This is present in ui_suite_dsfr_form_system_theme_settings_alter

Also in _ui_suite_dsfr_get_colors_options:

$theme = \Drupal::config('system.theme')->get('default');

It is loading the default theme, it should load the theme of the current settings form and no sub-theme management.

Maybe it is by design and I missed documentation that the colors should be duplicated from .info.yml to subtheme .info.yml.

Proposed resolution

Handle current settings form theme properly.
Allow sub-theme.

Remaining tasks