there is a place in northern spain , where i have found that there are lots of melanistic natrix natrix
i have not seen pictures of melanistic iberian natrix , sorry for the bed quality , i have seen more or less 15 natrix natrix in this are , full of heaths, ferns and oaks , the place is at 700 m height a.s.l
other species in the area are lacerta bilineata , podarcis muralis , natrix maura , vipera seoanei and anguis fragilis
dont know if you can see the pics
http://www.flickr.com/photos/49965750@N05/?saved=1