I don't know if you're trying to keep it traditional or not but most just use a traditional black Karate gi. To my understanding and I could be wrong a traditional Shinobi Shozoku (I think I spelled it right) is nothing more than a Hakama wrapped up with leggings and a Kimono top tucked in the hakama and a scarf type cloth used as a mask. Black wasn't normally used as this would stand out in the darkness. Something more in the line of dark blue, brown and maroon would do great for use in the dark. But the only reason they used this is that this is how people in Japan dressed like. So for modern days would be something that would allow you to hide in plain sight.....