If you want to change the color and/or style of a link in your email, you can use a style definition within the <a> tag.  To set the link style you will need to edit the html code.  Here is an example that removes the underline from a link and sets the color of the text in the link to white:

<a href="http://www.yoursite.com" style="color:#000000;  text-decoration: none;">Link Text</a>