The RSD12s, to my knowledge, didn't get any blue paint until they were converted to MT-6 slugs.
We used them as hump and pullout units at Selkirk after the PC merger. For the hump, they had them lashed up with former PRR GP9Bs (one RSD12 with two GP9Bs) that were in very bad shape by them. Let's just say it was difficult to keep the B units running much of the time. On the east end of the yard, single RSD12s worked as a "pullers" (usually 3 to a shift) to yank cars out of the bowl and make up trains on the departure tracks.
The RSD12s (along with a couple of PRR short-hood-lead RSD15s) were mostly supplanted in 1970 by the PC-ordered U23Cs. I seem to recall using the RSD12s, though, on the job that switched the local yard, right up until April 1976. A day or two after 4/1/76, we got EL U33Cs (with composition shoes!) to switch the locals. What a disaster that was!
It was an "interesting" time, what with cabooses heated with coal stoves showing up, along with the mostly worn out EL power that came around.
I didn't see much of the RSDs again until they had been cut down to slugs in the early CR era. I never saw a blue RSD12 or 15, that I can recall.
By the way, the PRR RSD12 units were originally equipped with steam generators for PRR passenger service.
