A lead came into Selly and I reply to the lead by email. However, the lead is still in green.

If you reply to an internet lead by going into the email module, click on the email that you got from the internet lead and press the reply option, but the lead is still in green when you go to the client module or the lead management module. It is possible that the person that's replying to that lead is not the person that the lead was assigned to.  

The best way to resolve this is to have the assigned rep reply to that lead.