The "FSN#" correspondences to the Fed Std 595 number. Which in some model paints #26270 is called Light Ghost Gary used on some US Aircraft as well.
Over the years there were several "Ocean Grays". There was an Ocean Gray in early 1941 in neutral gray paint with the initial WWII camo schemes. Then in mid-1941 a revised Ocean Gray 5-O made with the Purple-Blue paints was introduced and used for much of the war. Due to a shortage of the Blue Pigment used in the Purple-Blue Paints (5-N, 5-O, 5-H), the USN started to develop/switch to the Neutral Grays (#7 Navy Gray 5-N-NG, #17 Ocean Gray 5-O-NG, and #27 Haze Gray 5-H-NG)in very late 1944. The new paints weren't available until about February 1945 and even then "EXISTING STOCKS" were to be used first. Trying to figure out which ships were painted with what paints in 1945 leads to many arguments.
I didn't bother mentioning 5-O use in the 1950's because I wasn't sure how often it was actually used and when/where. I took it that #27 Haze Gray (in a few different formulations as the "color" remained the same, but the paint ingredients changed as lead was removed and other properties were incorporated, changing the faded appearance) was used almost universally. Your statement that your ship was painted in Ocean Gray is the first I have heard confirming its use. I have some images (scanned B&W photos) that I have suspected could have been painted in #17 Ocean Gray, but given variations in tones with B&W photos, I couldn't confirm that it wasn't due to film/print processing.
The use of #17 Ocean Gray may explain this image I scanned at NARA back in early June of US BOSTON (CAG-1) about 1956, early in her career as a "Guided Missile Cruiser".