This is a new feature of the version 4 groups.
In the Icon field you should be able to set one of these icons from these icon-fonts like material design. @tobiasdiez for sure knows exactly what you have to enter there.
And the color field sets the color of the field.
I could not yet figure out how to display an icon, but you can enter there some text and if you type "orange" (without quotation marks) in the color field, the text will be displayed in orange.
The changes appear when you expand/unexpand the groups once.