It should be a different color than the text so the visitor knows it's a link. If you increase the size of a link that occurs within text then it will make the lines uneven otherwise it shouldn't matter.
However using different formatting for links in different areas of the page can incur a lot of headaches if you are using CSS to format your links for someone unfamiliar with CSs, so the simpler the better .
Seems like everyone is commenting from the perspective of visitor functionality and they're right. With regard to search engine spiders, however, it shouldn't matter the size or color of your links because the spiders will just follow the hyperlink and take the anchor text into account for keyword, etc.