Jeep colours

[Jan Mostek]

The jeep shown below is pure american, but I guess it is very interesting because it in US Navy livery and of course, because the purpose for which it is used.

I would expect the US Navy vehicles to be painted blue gray with black lettering, this jeep looks to be ordinary olive drab. What is little bit strange to me is the black field under the USN letters. Does anybody have some additional information or explanation?