Actually, the dark green version is the 23761.
The 761 came in the normal light green associated with most semaphores. The dark green is a variation, usually in poor condition due to paint chipping as the chips are more visible on the darker paint. The 23761 is always in the lighter green. All boxed versions I have seen in 40 yrs are the lighter green. The black wire is the ground or base. It simply connects to the lug which is screwed directly into the base.