change the color of the inserted text while appending a text area field

Hi,

there is a text area in my form with some data in it. When a reviewer opens the form, on clicking review button, he makes changes in the textarea. WHat I want is the typed in charatcers should be in a different color.
can this be done.

for example
original text in the textarea: This is text message.
after Reviewer inserts text: This is a text message (the letter 'a' is included in the content)

In short, I want to implement MS-word's track changes feature in ASP.

Thanks in advance
sankari