sitefarm seed brand color application in a theme.

sfseed.settings.yml

article_category_field: field_sf_article_category
event_category_field: field_sf_event_type
photo_gallery_category_field: field_sf_gallery_category
branding_field: field_sf_branding
brand_color_field: field_sf_brand_color

sfseed.theme.php

<?php

/**
 * Fetch the category brand color name for a given node
 *
 * @param $entity
 * @return string - color name or bool FALSE if not set
 */
function sfseed_get_category_brand($entity) {
  $article_category_field = theme_get_setting('article_category_field');
  $event_category_field = theme_get_setting('event_category_field');
  $photo_gallery_category_field = theme_get_setting('photo_gallery_category_field');
  $branding_field = theme_get_setting('branding_field');
  $brand_color_field = theme_get_setting('brand_color_field');

  // Node.
  if ($entity->getEntityTypeId() == 'node') {
    // Articles.
    if ($entity->$article_category_field && !$entity->$article_category_field->isEmpty()) {
      // Grab the first category term.
      return $entity->$article_category_field->entity->$brand_color_field->value;
    }
    // Events.
    elseif ($entity->$event_category_field && !$entity->$event_category_field->isEmpty()) {
      // Grab the first category term.
      return $entity->$event_category_field->entity->$brand_color_field->value;
    }
    // Photo Galleries.
    elseif ($entity->$photo_gallery_category_field && !$entity->$photo_gallery_category_field->isEmpty()) {
      // Grab the first category term.
      return $entity->$photo_gallery_category_field->entity->$brand_color_field->value;
    }
    // Nodes with the Branding Taxonomy.
    elseif ($entity->$branding_field && !$entity->$branding_field->isEmpty()) {
      // Grab the first category term.
      return $entity->$branding_field->entity->$brand_color_field->value;
    }
    else {
      return FALSE;
    }
  }

  // Taxonomy.
  if ($entity->getEntityTypeId() == 'taxonomy_term'
    && $entity->$brand_color_field
    && !$entity->$brand_color_field->isEmpty()
  ) {
    return $entity->$brand_color_field->value;
  }
  else {
    return FALSE;
  }

}

/**
 * Implements hook_preprocess_node().
 */
function sfseed_preprocess_node(array &$variables) {
  $node = $variables['node'];

  // Set the category brand class color if it is available.
  $variables['category_brand'] = FALSE;
  if (theme_get_setting('use_category_colors')) {
    $variables['category_brand'] = sfseed_get_category_brand($node);
  }
}

/**
 * Implements hook_preprocess_page_title().
 */
function sfseed_preprocess_page_title(array &$variables) {
  $node = \Drupal::routeMatch()->getParameter('node');
  $term = \Drupal::routeMatch()->getParameter('taxonomy_term');

  // Check if the node is just a node ID. If it is then the page is a node revision
  // TODO: remove once https://www.drupal.org/node/2730631 is finished.
  if ($node && !is_object($node)) {
    $node = FALSE;
  }

  // Check first to make sure that this is an entity and not just a term id
  if (is_string($term) || is_int($term)) {
    $term = Term::load($term);
  }

  // Set the category class color if it is available
  if (theme_get_setting('use_page_title_category_color')) {
    if ($node) {
      $variables['category_brand'] = sfseed_get_category_brand($node);
    }
    elseif ($term) {
      $variables['category_brand'] = sfseed_get_category_brand($term);
    }
  }
}