The Drupal 7 branch of Jquery Colorpicker offers a form element than can be included in any form in this way:

$form['element'] = array(
  '#type' => 'jquery_colorpicker',
  '#title' => t('Color'),
  '#default_value' => 'FFFFFF',
);

This module includes Field API integration. A colorpicker field can be added to any content type with the JQuery Colorpicker widget

Drupal 6 is no longer supported, and will not be updated nor receive any bugfixes.

Concept

This module creates a new Form API element type: colorpicker, which relies on the 3rd party integration of the jquery colorpicker. After enabling this module and downloading the relevant files from the site linked above, a new form element can be created.

A Field API field is also created that can be attached to any fieldable entity.

This will automatically place the colorpicker into the form, allowing users of the form to choose a color from the jquery colorpicker.