the USAF is painting their Nighthawks grey. this is for operations at daytime. right now, they are all black, but if the tests with the grey "Black Sheeps" turn out well, they will remain in this colour.
They were probably still too black since the last repaint...
The original ones were deep black, couldn't fly with full moon, which infulenced gulf war 1 bombing raid planning too much got a lighter color after 1991 to cope with that and now another repaint
This is the third colorscheme of the F-117, the most-seen black scheme is actually the second. When they made it public they were in the first scheme, which was quickly changed into a lighter one. they were even darker before