The final column on the right shows the message status of a prospect. 

If the button is green and says “Unread”, it means that there is an unread message from this prospect that you need to view.

If the button is blue and says “Message”, it means that you have read any and all messages from this prospect. 

By clicking on either button, you can view the message history between you and the prospect. You may also reply or send a new message to the prospect within this window. If your prospect’s message has stopped it from completing the sequence, you can choose to “Continue sequence” at the bottom of the message window.