First off, I am an an active duty US Navy officer and have been building models since I was a kid. I have spent all of my sea time thus far on CG's, DD's, FFG's and DDG's, so my comments apply mainly to these types. What follows is probably more than you ever wanted to know about modern Navy colors.
I have seen this discussed at length and it amazes me how many people get it truly confused. This is tricky if you want to accurately model a ship as far as these colors are concerned and I would recommend working from photos. However, if you want to model your ship to represent 100% freshly-applied paint (very rare unless you are making it as it appeared at commissioning), you would need three colors (Haze Gray, Deck Gray and Non-Skid/Flight Deck Gray).
Haze Gray, as many of you know, is applied to all vertical surfaces of a ship's superstructure and masts (including VLS, antennae, launchers, etc). It is also applied to the hull down to the black boot topping. Haze Gray is usually consistent in color from batch to batch and when touch ups are performed by ship's force they blend in quite well. The reason you may see variation in this color of paint is due to weathering and the ship's departmental painting policies/priorities.
When freshly applied, Deck Gray (sometimes referred to as "Slick Deck") is a different shade of gray than the non-skid. It is used on all horizontal surfaces that do not require the tractive qualities of non-skid and you will typically see a thin band of it along -all- of the extreme deck edges (to help with water drainage), along panel lines on the decks (e.g. the edges of hatches and bolted panels so that they can be closed properly and sit flush), around the bases of almost all deck fittings (vents, scuttles, pipes, bitts, equipment bases, chocks, etc) and on horizontal surfaces that do not normally see human traffic (certain platforms, unused decks, etc).
Non-skid (Flight Deck Gray) paint has a somewhat purple hue relative to Deck Gray and is only applied over large areas by contractors (NOT usually Navy personnel), but it is almost as dark as deck gray. The non-skid material has abrasive particles mixed into a base paint and it is applied in such a way that deeply textured ridges are formed. Although this really helps with traction, it can also seriously injure you if you fall on it (MUCH worse than "Road Rash"). The application process starts with the grinding of the deck surface down to bare metal. Contractors work in large areas, so you will usually see the entire fantail being done, the entire forecastle, the flight deck, or the main deck (in sections). It is unusual to see all of these areas being re-done at the same time. After grinding the decks to bare metal, a primer is applied (typically tan, but it could be pale green). Once this primer is dry, contractors paint the edges of the deck, equipment bases, panel edges, deck equipment and other deck fittings (see list above) Deck Gray (much the same way you "edge" around wall fixtures and doorways when you paint a room at home). Once this edging of Deck Gray is applied, the non-skid material is mixed in large batches and applied to the remaining deck areas using special rollers that allow a certain texture to be created (it isn't just slathered on). Keep in mind that the non-skid is not usually applied all the way to the edge of the decks or the deck fittings and deck hatches...that is why they pre-apply the Deck Gray edging first. Despite the fact that some model paints are called "Flight Deck Gray", the flight deck, forecastle, main decks, fantail, and superstructure decks are ALL coated in the same kind of non-skid paint.
As stated before, the Deck Gray paint is slightly different than the non-skid as far as hue when freshly applied. It should also be pointed out that the non-skid surfaces weather and fade to a shade of gray similar to Haze Gray (yes, that light...almost chalky) after a short time while the edging and other "Deck Gray" areas remain relatively dark. The lines of "Proper Deck Colors" are further blurred on real ships when ship's force apply what is called "Deck Wash" to entire swaths of weathered and rusty decks. This "Deck Wash" is significantly thinned Deck Gray (about 50% thinner or more) and it is rolled onto the deck, covering -everything- (including the non-skid) in a uniform color. I have also seen sections of deck washed in a thin mixture of Black paint because it was all that was available.
"Deck Washing" is usually done by individual Departments or Divisions within each ship's CoC and as such, they only paint areas of the deck (and superstructure) that are their responsibility. It must be noted that if ship's force applies this wash to any portion of the deck that contains helicopter markings, helo ops for the affected area on that ship are technically de-certified for use. Take a look at reference photos...the helo deck and the forecastle/fantail VERTREP markings are usually untouched and faded while the decks around them are a different color due to touch-ups. So, in reality, you can actually observe a multitude of deck and superstructure paint differences/patches on real ships because each Dept or Div paints their areas when they need to. True, Navy regs say you are not authorized to paint for beautification only, but I defy you to find a ship in the fleet that doesn't do what I mention above to keep the ship looking good (even if it really doesn't help with preservation).
Wanting to be as specific as possible with my models, I took notes/photos/paint samples of the ships I have served on and the above discrepancies are EASY to spot. How you choose to paint your ship is up to you, but if realism is what you are after, have a closer look at the reference photos for your subject and I'll bet the decks and superstructure look like a patchwork of grays. If you ever wondered why, now you know.
HTH.
Mike