The helmet
It is basically the same helmet as the HGU-55/P but with a different visor and communications setup. The HGU-55/G helmet comes in three sizes, medium, large and extra large. The helmet has a gray leather edgeroll and gray leather ear cushions (elephant ears). The liner used is a two piece liner which is custom fit and covered with gray leather also. The helmet has a black neck strap and a black chin strap (British model) quick disconnect type. The receivers used are the normal lightweight type. The communications cord is the standard CX-4708A/AIC cable but with a slightly different plug. According to some sources, new HGU-55/G’s are delivered with TPL and black leather earcups.

a German F-4F pilot wearing his HGU-55/G helmet and MBU-5/P mask.

The Oxygen mask
The Luftwaffe uses the MBU-5/P, the MBU-12/P and the HA/LP masks with their helmet. The biggest difference visible on these oxygen masks is the WEA device at the left-hand side bayonet. The WEA (Wasser Entreglung Aktiefierungs Einheit) is a water activated opening device. This device contains a tablet that solves in water and that activates a spring to push the bayonet from the retainer. It only opens a little, just enough to prevent the pilot from drowning. When the mask would be still on the pilot's face, there is a chance of breathing water trough the oxygen hose. 

Close view of the WEA device attached to an MBU-5/P Oxygen mask

The German version of the MBU-5/P has a black hardshell instead of the common green one. Also noteworthy is the communications cord which runs from the mask to the end of the oxygen hose, being normally coiled the German Luftwaffe prefers a straight version.

The HA/LP is coming in to use more often and a special version is developed for use on the German MiG-29G aircraft. The HA/LP Mask is modified with the Russian Exhalation Valve. 
This was worked up while configuring the Gentex Sukhoi/MIG HA/LP Mask for the Czech Air Force. The GAF never provided Airworthiness Certification for this configuration but it is still in use. 

HGU-55G with HA/LP

The visor and visor cover
The visor consists of the distinctive German cover and a dual visor. The dark visor comes in two grades of protection, 15 or 25 percent, it is activated by a knob on the left hand top of the visor cover. The clear visor has a knob on each side and is activated by pushing one knob in and pulling the visor down. The other knob is only there to support the pulling down. The visor cover extends at the corners to prevent the parachute straps or cords during ejection. You can also find this type feature on US Astronaut and high altitude helmets.

"Exploded view" from an HGU-55/G 

Source: Ron Kraan, CSA