In 1989, the experiment to stop painting the upperworks in black was presented by NAVSEA to my ship as a "low observability" scheme. I was on a Knox class ship, so it had nothing to do with the propulsion plant. In 1987-88 USS Cook and a Spruance made a deployment and it was determined that the lack of black topmasts kept the ships from being seen for a difference of several miles. (It was commonly known that the topmasts of a Knox or a Spruance stood out in stark contrast to the horizon.) I don't know how widely or how quickly that change was implemented.
The Navsource photo at
http://www.navsource.org/archives/06/im ... 105315.jpg shows a mixture of black and grey topmasts on a bunch of 1052s after their decomm in 1992.
The NAVSEA folks made a point of telling us that the black had not been a Navy mandate but a custom that filtered from the Sixth Fleet/Second Flt in the 50s to the Seventh Fleet/Third Flt when the ships were deployed together around Viet Nam. Apparently the Sixth Fleet commanders saw the black upperworks on European ships and copied it. Or maybe that was just a story, with a couple of NAVSEA O-6s pulling our leg.
My ship (Stein, FF-1065) got the grey topmasts and at the same time, lost all black and white paint, as a measure against IR missiles. (The good Lord knows we couldn't defend ourselves with the weapons onboard - "shoot with the 5" until the incoming missile is in range of the BPDMS, then stop shooting 5" so we don't knock down our own outbound missiles" - good grief). So at that 1988-89 yard period, Stein had the hull numbers painted in dark grey/ light grey, the top of the ASROC mount became light grey, the bottom of the small boats became dark grey.
I know that in 1993 (July?) the dark grey/light grey hull number scheme was adopted fleetwide. Don't know how long that lasted.