Link to node icon appears not activated

I added the linktocontent module (version found here : http://drupal.fckeditor.net/download/linktocontent-fckeditor-6.x-2.x-dev...) for FCKeditor editor.
All works fine (I can add link to another page in the editor), but icon status for adding this link to content appears to be not activated status although it is really activated. The icon colors are attenuated relative to the icon distributed in the .zip (linktonode.gif).

How can I change this to make this icon active ?

thanks for your help.