It gets more complicated if you want to dynamically change text within one text field. You can format parts of a text object manually using the format toolbar buttons, but these don't let you do it dynamically. The only way I know of to do this is to use a formula that outputs an HTML string that uses the Font tag. Then tell the text object to display it as HTML.
The string would have to by something like this
My Name Is <font color='red'>Peggy</font>
You would have to incorporate these font codes into your formula so that you can change it as needed.
HTH.