Color::validateColor

public static Color::validateColor(&$element, FormStateInterface $form_state, &$complete_form)

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.', array('%name' => empty($element['#title']) ? $element['#parents'][0] : $element['#title'])));
    }
  }
}