The grey bars displays the directions which is controlled by the respective input side (IN) of the gate. In the picture on the right, the right input side controlles the signal direction from the lower bus to the upper bus, and the left side controlles the signal direction from the upper bus to the lower bus.
If a redstone signal recieves about a bundled cable the lower bus of the gate, then the signal is only transmitted to the upper bus, if the blockage is removed through a redstone signal receiving the right input side (IN). The left input side has no influence in this direction, it controlles all signals from the upper to the lower bus.
Additionally, the two displays on the cables shows the active channels of each controlled bus input.
Using the screwdriver from Project Red, the orientation of the gate can be changed freely in all four directions. With additional holding the crouch key you can switch the sides for the respective blocked direction.