Which light. Not sure what you mean by the "100 or 1000 network" ? The color of the light typically means whether or not the modem is locked on to multiple bonded channels. What you posted shows that it is and everything is normal / in spec.
O/k that's an ethernet port / LAN light. It's on your network / LAN and has nothing to do with the Comcast connection / system.
So what ever device it is that you have connected to that port is not negotiating a gigabit connection. Does the device have a 10/100/1000 gigabit capable NIC / network adapter ? Check the integrity of the ethernet cable as well.
FWIW, they can not change the port negotiation speed / color of that light on your LAN / computer remotely. Something else is going on. Perhaps that port / gateway device is malfunctioning. Have you tried another port on the gateway ? No joy ? Get it swapped out for another. There could also be something intermittent going on with your computer's NIC / network adapter / ethernet port.
Good luck with it !