Hi,
the CSS class is named .interwiki, you can change it by overwriting it in your <dokuwiki>/conf/userstyle.css (if this file doesn`t exist you have to create it), this way you can make your changes upgrade safe. ie:
div.dokuwiki a.interwiki {
color: #yourcolor;
}
div.dokuwiki a.interwiki:hover {
color: #yourcolor;
}
chi