Color the rims of the balaclava, probably with paint, or if you can sew a bit, there is time to take black thread to the edges of the openings to make them the shapes you need. Using white paint on the black pantyhose to make the gap at the mouth would fix that problem.
ETA: The biggest thing with using black under white would be ensuring how dark the hose would look worn and matching the embroidery/paint.
I’d use the black marker on the white lenses. Should just soak right in to the fabric and not affect vision at all. Then I’d use black fabric paint on the other areas where vision isn’t an issue.
You might also email the seller and ask if he has any like that in solid black. The do the artwork with white paint.
re: the neck, a black or white strip of cloth choker would be perfect.
Another thought, if you know someone handy with sewing gear you have plenty of time to pick up some fabric and have them whip you something together.
An interesting idea. Is there any reason to go black instead of white? Remember that Rorschach’s mask is mostly white.
I did a Rorschach costume when I was in high school, so it’s been about 20 years, but IIRC my mask was made from a white pillowcase, on which I used a fabric marker to draw in the black spots. Obviously, the spots did not move.
No holes for eating or breathing (I just breathed through the fabric), and the material was just sheer enough to see fuzzy shapes so I didn’t walk into anything. It was not the most pleasant costume of all time, but I like to suffer for my art. 
Despite the non-moving, clearly drawn-on spots, you’d be surprised at how effective a mask that has no holes is. It disturbs people to look at a face and not be able to see the features.
Because if the mask is solid black you don’t need to figure out how to make the eye area black while still being able to see through it.
But if anyone hits on you, don’t forget to drop them down an elevator shaft. {Couldn’t you just strip off, paint yourself blue and go with your willy hanging out as Doctor Manhattan?}
Get it in white and then do the design in black.
What Otto said. I believe it would be easier to fill out the mask with an opaque white fabric paint than trying to darken the sheer eye panels. You couldn’t use a paint for that because it would make the fabric opaque.
A zentai suit mask is perfect. See the black version here: http://cgi.ebay.com/Lycra-Zentai-black-hood-mask-over-all_W0QQitemZ190155315492QQihZ009QQcategoryZ36306QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
Zentais are MADE for costumes like this, and I’m pretty sure with some searching you can find a white version and buy just the mask. They tend to be made as a full body suit and marketed for cosplayers or as fetish gear, so target your search with several applicable keywords. It’s going to be easier than pantyhose and they are made to be work on the face, so will likelier be more comfortable.
Elysium, while that looks like it would be perfect, if sounds from the question and reply here like vision is severely impared. I’ll keep this in mind but I really would like to be able to see as clearly as possible.
How big does the grapple need to be? Here is a four prong cleaning hook horse fanciers use. It’s about a foot long.
Why don’t you go as Walter Kovacs instead? Making a “the end is near” sign is easier than making the mask. Use red hair spray et voila.
Here we go. Can you afford to pay $50 for it?
http://tinyurl.com/22ep4z
If not, why not just paint your face white and black. It would do.
or, for a home made effort: http://www.surlyrobot.com/?p=171#comments
One final touch your costume needs - a dried rose.
I don’t know. Buying a premade mask would feel like cheating after all the thought I’ve put into how to make one. Besides, I’d have a bit of trouble justifying $50 bucks for a mask.
That sounds perfect. Thanks for the link. I’ll have to give it some looking into.