Hi John,
I did change the colors hexa, refresh browser and cache and so on
But no change
I'm not sure having wrote the code in the proper place
I did it here, in template.css file :

/* Begin Additional CSS Styles */
.headline, .headline a, .headline a:link, .headline a:visited, .headline a:hover

#jmap_sitemap { background: -webkit-linear-gradient(top, #FF0000 0%, #00405C 100%) !important; background: -o-linear-gradient(top, #FF0000 0%, #00405C 100%) !important; background: -ms-linear-gradient(top, #FF0000 0%, #00405C 100%) !important; background: linear-gradient(top, #FF0000 0%, #00405C 100%) !important; }
}



/* End Additional CSS Styles */

is that right ?