When we are replying, it is prefixed with '>' to indicate that it is Old text...

Apart from that if the original message is :-

1. Prefixed with '>' (which it is already doing)
2. Bold = .f.
3. Italics = .t.
4. Color=Different than black (green/grey/blue )

& Replied message

1. Bold = .t. (which is already there)

This will give a visual clue to user what was the new text added & don't have to read/search the full message....