Martha "Mattie" King was from Maryland, which of course was not a Confederate state, though there were certainly Southern sympathies in the area. I have not read that Mrs. King was the source of inspiration for the gray uniform. It is recorded in several sources that ADM King never favored the working khaki, which he considered a land-forces uniform. The khaki was still pretty new to most of the fleet, having been authorized in early 1941, and king considered it to be only a "stopgap." He began working on a replacement soon after he got the CNO post in the spring of 1942. After a trip to Britain in July 1942, he expressed admiration for the RAF's blue-gray uniform, and soon had a tailor work up a naval uniform in a gray version of the Marines' herringbone twill fabric.
Despite protests from the Bureau of Supplies and Accounts, King obtained Secretary Knox's approval for the gray working uniform in April 1943. After that date, working khaki officially entered a phase-out period. There was so much khaki material in the supply system, however, it outlasted King's tenure. His successor, FADM Nimitz, wasted no time reestablishing khaki as the standard working uniform and it was the grays' turn to enter a phase-out period. Working gray could not be worn after October 1948.
Five-star gray shoulder boards are understandably rare. King, of course, wore them, as did FADM Leahy, as grays were common in Washington where King held sway. After 11 August 1943, the standard gold shoulder boards were authorized to be worn with working gray along with gilt buttons. Leahy wore this uniform at the QUADRANT conference in Quebec in August 1943, he is standing on the right:
King, curiously, is wearing blues, while Admiral of the Fleet Pound is in whites.
FADM Nimitz was known to abhor the gray uniform, and it was unlikely that he ever obtained a set. FADM Halsey is questionable, though I would say it is also unlikely. Gray remained unofficially banned in the Pacific, though it did occasionally make an appearance:
Admiral King was known for tinkering with uniforms. When he was CO of USS
Lexington he prescribed a uniform of white blouse with blue trousers and black shoes. Though his officers didn't like it, he brought it back when he was Commander Aircraft Battle Force, and when he was CNO made it official navy-wide as "Service Dress E." He also instuted wearing the light gray shirt with collar insignia with the service blues, and had his own non-regualtion dress whites, cut like khakis with a shirt and tie.
Best regards,
Justin