Group Node Socket Type in this tutorial about a Specular Workflow at about 14:10 min a Reflection Node Group is shown. You can see a socket named Specular and you can see that yo can change the value of this socket



Looking at the Node Group in detail you can see that the Specular socket of the Group Input node is connected to the Color1 socket of the Mix node. Clearly the Specular socket is a color field. 



Question I don't understand how it is possible that while the Specular socket is a color socket it is possible to enter values in the Specular socket. If I create this node group this is my Reflection Node Group. In my Specular socket you can only enter a color and not a number.How can I change the Specular socket from a color socket to a "value" socket ?
I now understand that you can create a value socket in the Group Input node. This can be done in two different ways:

1) create a Value node and connect it to a Group input socket. Then you can reconnect that Group Input socket (with color grey) to a Color socket in your node group

2) you can duplicate an existing Group Input socket (value socket), rename it and connect this value socket to a color socket in your node group