The low sun angle on Groot's posted photo of Peleliu makes the deck appear darker of course, and fresh from a yard availability the deck would be dark, but never black. Even in Groot's photo you can see the deck looks more "gunship grayish" than any shade of black.
Model builders can make their flight decks any color they'd like, but I just so often see ship models of CVNs, LHAs, LHDs, etc., with coal-black flight decks. In reality, the decks just aren't that dark.
The navy.mil photo gallery is a wonderful source to judge ship appearance in various lighting conditions, and stages of wear and tear.
While it is more apparent on CVNs than the gator ships, you can often see patterns in the flight deck non-skid. Since the big carrier decks don't often get a full covering of non-skid at once, you can often see block areas of the decks in lighter and darker shades, usually with a rather sharp demarcation line between them. You can see different gray shades even under freshly painted markings. The non-skid fades quickly in sunlight. You don't notice these differences on the gators as often.
It is subtle, but makes a very nice touch to use such details on a model containing such large surfaces. It breaks up the monotone look and adds a little challenge to the painting.
Surface_Line's idea of using the aircraft color dark ghost gray for the hull of an LHA is an interesting approach. The FS 26270 reflects the water's color and often adds blueish tones to the hull depending on the light, etc. That could be an elegantly simple way to depict that effect.