[css] CSS: How to change colour of active navigation page menu

I think you are getting confused about what the a:active CSS selector does. This will only change the colour of your link when you click it (and only for the duration of the click i.e. how long your mouse button stays down). What you need to do is introduce a new class e.g. .selected into your CSS and when you select a link, update the selected menu item with new class e.g.

<div class="menuBar">
    <ul>
        <li class="selected"><a href="index.php">HOME</a></li>
        <li><a href="two.php">PORTFOLIO</a></li>
        ....
    </ul>
</div>

// specific CSS for your menu
div.menuBar li.selected a { color: #FF0000; } 
// more general CSS
li.selected a { color: #FF0000; }

You will need to update your template page to take in a selectedPage parameter.