fWidgetFormInputColor.class.php

<?php

class sfWidgetFormInputColor extends sfWidgetFormInput
{

  protected function configure($options = array(), $attributes = array())
  {
    parent::configure($options, $attributes);

    $this->setOption('type', 'color');
    $this->setAttribute('style', 'width: 30px');
  }

  public function render($name, $value = null, $attributes = array(), $errors = array())
  {
    if ($value && $value[0] != '#')
      $value = '#' . $value;

    return parent::render($name, $value, $attributes, $errors);
  }
}

sfValidatorColor.class.php

<?php

class sfValidatorColor extends sfValidatorRegex
{
  const REGEX_PATTERN = '/^#?[a-f0-9]{3}|[a-f0-9]{6}$/i';

  /**
   * @see sfValidatorRegex
   */
  protected function configure($options = array(), $messages = array())
  {
    parent::configure($options, $messages);
    $this->setOption('pattern', self::REGEX_PATTERN);
  }

  protected function doClean($value)
  {
    $clean = parent::doClean($value);

    if ($clean[0] == '#')
      $clean = substr($clean, 1);

    if (strlen($clean) == 3)
    {
      $tmp = $clean;
      $clean = $tmp[0] . $tmp[0] . $tmp[1] . $tmp[1] . $tmp[2] . $tmp[2];
    }

    return strtolower($clean);
  }
}