Tom,
This question has been asked many times. (You can review all the past entries in this thread for the discussions) From photos of Nicholas taken just prior to her going to the South Pacific after she was painted in Ms 18 at Boston during August 1942 and textual records that O'Bannon was repainted the week AFTER Nicholas at Boston in an unidentified "new camo paint scheme" ... I'm sure that neither of those two were painted in Ms 12 mod upon arriving in the Pacific. Fletcher was upgraded with a second twin 40-mm mount on the fantail at New York the last week in August. There are no photos of her available from early August until about January 1943 to indicate her camo. But, orders were sent out to the destroyers in the Cactus force to repaint into Ms 21 in early November. NONE of the Fletchers that followed the first three were painted in Ms 12 mod. Some arrived to the South Pacific in Ms 22 or Ms 18.
Many of the early Fletchers prior to August 1942, were delivered and served for a time in Ms 12 mod as they worked up and performed local escort missions on the East Coast.
Nicholas arrived in the South Pacific "war zone" on 14 September 1942 and apparently repainted (or finished painting) on 12 November to Ms 21 (War Diary entry). O'Bannon and Fletcher arrived at the beginning of October 1942. Information from crew members say that O'Bannon repainted in early November 1942 to Ms 21. I don't know what camo Fletcher was painted to prior to early November ... but after the first of November she was likely painted in Ms 21. I have not taken the time to dig into Fletcher's records at NARA to see if more light can be shed on this area, but I have found it hard to find camo info on these ships in textual records to be sparse. But, there may be a Depart Report from New York Navy Yard that would indicate IF she was repainted in the end of August. At this time no one knows what Fletcher's camo was when she arrived in the South Pacific. My personal feeling is that it is unlikely that she was painted in Ms 12 mod. But, I don't know.
By the way, the often published image of Fletcher's Starboard side on 26 March 1943 that seems to show her partially still painted in "Ms 18" ... doesn't show the whole story. Here is a portside view taken at the same time. I think the "lighter" shade of paint seen on the starboard side is primer.
USS Fletcher (DD-445) on 26 March 1943