The Naval Infantry of World War II wore black – black tunic/shirt, black trousers, black boots/shoes, black hat (although it had a white trim). The ammo belts were whitened canvas with rounds pushed through them. This is one of my WW2 Painting Guides.
This is what I painted mine, and indicates the order as well:
|Tunic, Trousers, Cap, Boots||
Dry brush a mix:
212 Dark Grey (2 Parts)
102 Black (1 Part)
|Wood on Rifle||218 Wood Brown|
|Metal on Guns||
220 Silver (1 part)
212 Gun Metal (1 part)
|Belts||534 Dark Leather|
|Trim on Cap||101 White|
|Pouches and strap||502 Field Drab|
Check out BattleFront: Naval HQ and Platoon for how they looked.
As their uniforms wore out the Naval Infantry were issued regular army uniforms, and units could have a mix of naval and army kit. Check out BattleFront: Head Swaps on Soviet Naval Troops for a good example of such a mixed unit.
Check out http://rkka.ru/uniform/files/i_vmf.htm