I am not totally sure what you are trying to do, but I can't help thinking you are going about it the wrong way.
If what you are trying to do is replace the link text that is shown to the user in
<a href="www.brown.com">Brown</a>
so it becomes
<a href="www.brown.com">Green</a>
then why not try something a bit simpler:
(?<Tag><[^<]*>)|(?<data>[^<]*)
which breaks it into groups: those with tags, and those without.
You can then only change the "data" group items.
If that isn't what you are trying to do, then please give us better detail.