Note that the safety valve cover is painted green.

Peter Kerslake adds "Even a "Taffy Tank" could look its best when fresh from overhaul at Swindon and had been turned out resplendent in new fully lined green livery, as 6664 shows here in this image from June, 1957, the year when the first examples were turned out following overhaul from Swindon initially in unlined green livery and then, as seen here, fully lined out.
My shedbook shows that 6664 had been allocated to Slough in 1956, although the majority of the class were based in South Wales, the final fifty of the class having been built by Armstrong Whitworth at Scotswood on Tyne from 1928.
Well used on both freight duties and passenger workings the Welsh based examples of the class were popular with footplate men when working local passenger rosters through the Welsh valley lines, invaraibly running bunker first on their homeward run when no turning facilities were avaiable at the destination at the end of the outard run.
The sliding cabside shutter is clear to see in this image, an essential protection for footplate crews during the Welsh winters, especially when working bunker first "