In February 1945 the US Navy discontinued the use of the purple/blue camouflage colors, substituting neutral gray tones. This included changing 5-H Haze Gray to a neutral gray. This neutral gray eventually became the fore runner of the the modern US Navy Haze Gray (FS 26270).
Testors naval paint 2156 is the earlier 5-H Purple/Blue Haze Gray. The 2153 "Natural" Haze Gray is more than likely the later color and designated as such so as to not be confused with Neutral Gray 1725 (FS 36270)