I don't see a way to edit the link color of the "Powered by Coppermine" link, but regardless of there is a way or not I think the future there should be the option on the admin panel to use the little coppermine button instead of the text link. Just think it would look better.
- RCS
You should be able to change it with CSS, it will respond to the 'footer' class. Feel free to submit a feature request.