Link Colour in Twenty Twelve

start by installing a plugin for custon css (if you are only planning to make formatting customisations) or by creating a child theme of Twenty Twelve (if you are planning to edit the templates as well).

http://wordpress.org/extend/plugins/search.php?q=custom+css

http://codex.wordpress.org/Child_Themes

you can use a browser inspection tool (such as Firebug for Firefox) to find out where and how the title links are formatted in style.css of the theme.

I just firebug-ed your site and can’t find anywhere defined #000 in it.

You need to modify color accordingly in following code:

a {
	color: #21759b;
}
a:hover {
	color: #0f3647;
}

You also have a syntax error in your style.css file. You can try adding to the bottom of the stylesheet:

body {
 border: 10px solid red;
}

And nothing will happen.

Please do not edit the theme’s files, it is vital to have a non-editied version of the default themes for debugging.

Move all of your CSS modifications in a Child Theme or Custom CSS plugin .

I investigated the syntax error in your style.css and found 3 syntax error.

On line 1747, 1750, 1753 : You forget or accidentely removed closing curly bracket }.

Yes, use a code editor like Notepad++.

Try using Firefox with the Firebug add-on for this kind of CSS troubleshooting. Or use whatever developer tool is available in your web browser.