There are a few green colours, describing how 'fast' is the terrain in the certain place. The more dark the green colour is, the thicker the forest is. White colour means the 'fastest' forest. That would be a control point all about the theory. Now a few words from the technical point of view.
First thing is how the control point looks in 'real life'.
Usually it is made of two pieces of pipe welded together to make a T shape. Below the punchers there is a sign with a number of the control point. This is to distinguish control points in the woods - usually during competitions there are plenty of control points standing sometimes very close to each other. During night competitions, on the sides of the lantern some phosphorencing substance is put on. The next thing is the confirmation of visiting a control point.