Thank you for your quick answer.
I finally obtained what I wanted with the following code : the color of the link of the current page is forced, whatever its location in the navigation menus.
Do you think of any side effects ?
.meta a { color: #55d737 !important; }
.meta a:hover { color: #55d737 !important; }
.current-menu-item a { color: #55d737 !important; }
.current-menu-item a:hover { color: #55d737 !important; }
Can I check the CSS of the right selectors through the page code from the browser ?