Unfortunately, there's not an easy way to change the font/color of the links on a per-link basis.
What most do is add a small 'new' or 'updated' icon to the link using something like img="/images/new17.gif" align="right"
to the <item ... /> description of the link.
I've attached my 'new17.gif' that you're welcome to use if you like. Just make sure the image is small (<15px high).