You may have reached this page like I did by selecting “configure plugins” from the admin screen, and then selecting “color” and then clicking on the link provided by the info for the color plugin.
If so, you may be looking for this page
No, actually, I got to this via a Google search for a tutorial on writing dokuwiki plugins.
Note: Information on writing plugins is available at: http://www.dokuwiki.org/plugins#creating_plugins