Web gear, webbing, 782 gear, Deuce gear- all names for the combination of belt, harness and various pouches that a soldier or Marine in the field wears in order to carry immediate and essential items like ammunition, canteens, first aid supplies, and other necessary bits of kit.
It is distinct and separate from the back pack that an infantryman carries, which contains less frequently used things like food, bedroll, shaving kit, a shelter half and so forth.
Apparently, it is traditional in the Royal Marines to blacken the webbing. I am all for tradition in the forces, as long as it isn't something that might compromise one's acheivement of the goal at hand.
Here is an example of Royal Marine kit blacked as described:
http://www.britains-smallwars.com/Museum/Suez/webbing.html