olivesimagined/olivesimagined.post_update.php

<?php

/**
 * @file
 * Post update functions for Olivesimagined.
 */

/**
 * Sets the default `base_primary_color` value of Olivesimagined's theme settings.
 */
function olivesimagined_post_update_add_olivesimagined_primary_color() {
  \Drupal::configFactory()->getEditable('olivesimagined.settings')
    ->set('base_primary_color', '#1b9ae4')
    ->save();
}