One problem with modern Haze Grey being the same as #27 neutral grey is that modern haze grey is not a neutral grey. The RGB shown for 26270 is R = 137; G = 143 and B = 145. So modern haze grey is a blue grey not a neutral grey. A neutral grey should have the same number for Red, Green and blue.
It could be debatable.
I have spent some time over the years looking into it all. Here's what I have found...
The Federal Standard Color System was introduced in 1956. From that point on, the color the US Navy calls Haze Gray was FS 26270. Under the current AMS 595 standard introduced in 2017, it is still numbered 26270.
Current AMS 595: https://www.sae.org/standardsdev/colorchips/
Prior to the 1956 FS 595 standard, the US Navy was using a Haze Gray called #27 Haze Gray. That came directly out of the WWII "Neutral Grays" color system, developed late in the war due to shortages of blue tinting material it had been basing its paints on. On the Researcher at Large site, there is a copy of the 1946 fleet-wide order to paint all US Navy vessels in Measure 13, using #27 Haze Gray. Post-war (early 1950s) painting instructions are also available online, and call for #27 Haze Gray.
Now for the debatable part...
Based on what I have found, I contend that #27 Haze Gray and FS/AMS 26270 are all the same color. I do so based solely on a "paper trail." I have never actually visually compared good/ accurate/authentic samples of the two. From some who have, they claim to see a difference. However, I have had a Navy vet, who did a fair share of paint ordering and supervision in his service, tell me a long time back that they were the same color. As well, I have found (online) official paint suppliers for the US Navy labeling their cans "#27 Haze Gray" and stating it satisfies Navy requirements for Haze Gray 26270.
Further still, I came across a table in a current Navy painting guide listing "the Navy names" for a list of AMS colors. AMS 26270 is listed in that document as #27 Haze Gray.
It would be important to note at this point that the Federal Standard and AMS colors have no official names; only numbers. So, in that same painting guide I just mentioned above, an earlier page lists all the AMS numbers the document will cover, and gives them "commonly called" names. IIRC, in this section, it lists AMS 26270 as Neutral Gray. However, it specifically notes that Navy names for the colors will be found in a following table, and that table is titled as such...Navy names for "the following" AMS numbers. As noted, 26270 is #27 Haze Gray.
That's what I have found. So... IF there is a difference, then "modern" Haze Gray 26270 was introduced with the FS 595 system in 1956. Before that, it was late wartime #27 Haze Gray. IF there is not a difference (and I have laid out why I don't think there is) then the Navy never switched... "Modern" Haze Gray is the old late war Neutral Gray #27 Haze Gray, just given a new designation when FS 595 came out in 1956.
When was modern haze gray introduced into the fleet after the war?