Color.php

<?php

namespace Drupal\Core\Render\Element;

use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Render\Attribute\FormElement;
use Drupal\Core\Render\Element;
use Drupal\Component\Utility\Color as ColorUtility;

/**
 * Provides a form element for choosing a color.
 *
 * Properties:
 * - #default_value: Default value, in a format like #ffffff.
 *
 * Example usage:
 * @code
 * $form['color'] = array(
 *   '#type' => 'color',
 *   '#title' => $this->t('Color'),
 *   '#default_value' => '#ffffff',
 * );
 * @endcode
 */

#[FormElement('color')]
class Color extends FormElementBase {

  /**
   * {@inheritdoc}
   */
  public function getInfo() {
    $class = static::class;
    return [
      '#input' => TRUE,
      '#process' => [
        [
          $class,
          'processAjaxForm',
        ],
      ],
      '#element_validate' => [
        [
          $class,
          'validateColor',
        ],
      ],
      '#pre_render' => [
        [
          $class,
          'preRenderColor',
        ],
      ],
      '#theme' => 'input__color',
      '#theme_wrappers' => [
        'form_element',
      ],
    ];
  }

  /**
   * Form element validation handler for #type 'color'.
   */
  public static function validateColor(&$element, FormStateInterface $form_state, &$complete_form) {
    $value = trim($element['#value']);

    // Default to black if no value is given.
    // @see http://www.w3.org/TR/html5/number-state.html#color-state
    if ($value === '') {
      $form_state
        ->setValueForElement($element, '#000000');
    }
    else {

      // Try to parse the value and normalize it.
      try {
        $form_state
          ->setValueForElement($element, ColorUtility::rgbToHex(ColorUtility::hexToRgb($value)));
      } catch (\InvalidArgumentException $e) {
        $form_state
          ->setError($element, t('%name must be a valid color.', [
          '%name' => empty($element['#title']) ? $element['#parents'][0] : $element['#title'],
        ]));
      }
    }
  }

  /**
   * Prepares a #type 'color' render element for input.html.twig.
   *
   * @param array $element
   *   An associative array containing the properties of the element.
   *   Properties used: #title, #value, #description, #attributes.
   *
   * @return array
   *   The $element with prepared variables ready for input.html.twig.
   */
  public static function preRenderColor($element) {
    $element['#attributes']['type'] = 'color';
    Element::setAttributes($element, [
      'id',
      'name',
      'value',
    ]);
    static::setAttributes($element, [
      'form-color',
    ]);
    return $element;
  }

}