Hi Eddie
I guess the 'brownish caste'  you refer to is what the manufacturer calls a 'slightly stronger warm tone' in their specification for that filter.  The filter was designed for photographing industrial processes that radiate a lot of light and heat eg steel blast furnaces and is optimised for that use. 
You have tried experimenting with the white balance to get an acceptable colour and that is probably the solution, by trial and error.  Perhaps shooting a white or grey card first, in the same light, before commencing shooting to get a level which you can correct with white balance adjustment in the RAW processing would be the surest method.
The vignetting doesn't surprise me with that lens as any filter fitted to it if used at its widest 10mm focal length needs to be extremely thin to avoid encroaching on the field of view. I use the Lee filter system, with that lens but I have to use their wide angle adapter that holds the filter virtually against the front of the lens.  Their standard filter holder will vignette at 10mm even though is is no more than a couple of mm thick.  I would be surprised if you could find a standard screw on type filter that didn't vignette. 

Curiosity is gonna cost me I expect,   but may I ask why you would use a 10stop ND filter on a scene such as above ?

Richard. 

 

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html