Drupal 8 allows for the configuration of theme-specific settings. These can vary based on the theme and the amount of extensibility that a theme provides. For example, if we click on the Bartik theme, we will note that it provides us with an ability to change the COLOR SCHEME through a series of presets, whereas the Seven theme does not.
Keep in mind that contributed themes installed in Drupal may provide additional configuration options, so it is important to both look at the README file that comes with the theme and check the settings for that theme to ensure that it's configured properly.