If you google NAVAL BRIGADE ZULU WAR,
you will see many useful images.
As to the buttons, I am not really sure, but I am inclined to think that they were really Royal Navy Buttons, or possibly General Srvice Buttons.
With regard to the helmets, they were indeed stained a definitely dark brown , using either Tea, Coffee or most probably just mud!
Just compare the grey tone of the helmet with the dark "navy" blue of the tunic in the B/N photos: they look more or less the same tone, so the helmets were really a dark colour!
Ast to the blue helmet puggaree/veil seen in photos and prints of the Egyptian and Sudan campaigns, it does not seem to have been so popular in the Zulu War, judging from photos, and contemporary prints I have seen.
Have a look at the 3 (rather well known!) attached pics: you can only see one puggaree/veil loosely wound around one officer's helmet, and this is definitely too light a colour to be blue: almost surely it is white , since it is exactly the same tone as the officer's white jacket
Congratulations for your Webley Bulldog: I would love to have one! Any chances we may see any pics?
Hope this helps.
PS: A couple of months ago, I was also contemplating to re-enact as a Naval Brigade officer , Sudan 1884-1885 , and I did spent some time in researching uniforms and equipment.
Eventually , though , I dropped the idea: seeing me in a blue reefer jacket and white trousers , most of my friends probably would not have resisted the temptation of sticking on me the nick of Captain Schettino
, of Costa Shipwreck fame!!!