|Draft -> Utilities -> VisGroup|
This command creates a special kind of FreeCAD group, with additional features: It allows to control visual features of the objects placed inside the group, such as line width, line color, shape color and transparency. By changing these properties on the VisGroup, the changes are propagated to the objects contained in the group.
The VisGroup can also be used on Drawing pages. You can then use it to control the color and linewidth of some Drawing Views. In that case, though, not all options are available, since, at the moment, Drawing Views don't support shape color or transparency.