WordPress single page, categories and archives menu current item

I was wondering if someone can help me with the following, as I cant get my head around how to do it!

On my website I have a menu:

Home | About | Skills | Portfolio | Contact

To call the above menu I have the following in my header.php file:

<nav>
             <?php wp_nav_menu( $args ); ?> 

        </nav>

At the moment when the page is active the link’s background color changes, here is the CSS and HTML generated:

header ul li a
      {
border-radius: 4px;
    background-color: transparent;
    border: 1px solid transparent;
    color: #939393;
    margin: 0px;
    border-image: initial;
    padding-left: 5px;
    padding-right: 5px;
    padding-top: 3px;
    padding-bottom: 3px;
    font-size: 18px;
    text-decoration: none;
      }

    header ul li.current-menu-item a,
    header ul li a:hover
      {
    -moz-border-radius: 4px;
    -webkit-border-radius: 4px;
    -o-border-radius: 4px;
    -ms-border-radius: 4px;
    -khtml-border-radius: 4px;
    border-radius: 4px;
    background-color: rgba(0, 0, 0, 0.042);
    border: 1px solid rgba(0, 0, 0, 0.15);
    margin: 0;
    border-image: initial;
    padding-left: 5px;
    padding-right: 5px;
    padding-top: 3px;
    padding-bottom: 3px;
    color: #939393;
      }

    header ul li.selected {
    -moz-border-radius: 4px;
    -webkit-border-radius: 4px;
    -o-border-radius: 4px;
    -ms-border-radius: 4px;
    -khtml-border-radius: 4px;
    border-radius: 4px;
    background-color: rgba(0, 0, 0, 0.042);
    border: 1px solid rgba(0, 0, 0, 0.15);
    margin-top: -3px;
    border-image: initial;
    padding-left: 0px;
    padding-right: 0px;
    padding-top: 3px;
    padding-bottom: 3px;
    color: #939393;
     }

Heres the HTML generated:

<nav>
   <div class="menu-main-navigation-container"><ul id="menu-main-navigation" class="menu"><li id="menu-item-42" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-42"><a href="http://localhost:8888/paulkenyon/home/">Home</a></li>
   <li id="menu-item-41" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-41"><a href="http://localhost:8888/paulkenyon/about/">About</a></li>
   <li id="menu-item-45" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-45"><a href="http://localhost:8888/paulkenyon/skills/">Skills</a></li>
   <li id="menu-item-56" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-56"><a href="http://localhost:8888/paulkenyon/portfolio/">Portfolio</a></li>
   <li id="menu-item-49" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-49"><a href="http://localhost:8888/paulkenyon/contact/">Contact</a></li>
   <li id="menu-item-52" class="menu-item menu-item-type-post_type menu-item-object-page current-menu-item page_item page-item-50 current_page_item menu-item-52"><a href="http://localhost:8888/paulkenyon/blog/">Blog</a></li>
   </ul></div> 

        </nav>

The above works fine, but what I am trying to achieve is when the user clicks on a blog post or archive or selects a category I want the ‘Blog’ link to remain highlighted with the different colored background-image.

At the moment nothing shows.

Is there a function I can use that states all single, and archive pages to highlight the ‘blog’ anchor?

I hope the above makes sense.

If anyone could help it would be greatly appreciated! 🙂

Thanks in advance