Phil
The narrow gauge engines were always grey, all through GSR and CIE times. Several, especially on the C & L, didn't receive a new coat of paint from pre 1925 days until well into the thirties, but that's not the same as GSR or CIE painting them differently.
While on the T & D, every locomotive was plain grey, without exception. T & D Nos. 3, 4 & 6 were on the C & L (can't recall if other T & D locos went there too), and all were grey on arrival. No. 6, at least, appears blackish in one good colour photo I've seen, but on closer inspection - on the very few clean bits there are - grey is evident. On coal trains, with coal dust flying about at Arigna, and smoke drifting about Ballinamore shed, aided and abetted by an almost total lack of any sort of cleaning, grey could look almost like a dirty black pretty quickly.
The shade is like a dark wagon grey; if you look at recent colour pictures of the RPSI's 186, that's very accurate. Watch, however, the smokebox - apparently, many at Whitehead thought that a grey smokebox and chimney looked odd, so they tended not to clean it like they did the rest of the loco, giving an impression in some photos that the smokebox is black! But it isn't, and wouldn't have been; the GSR / CIE grey encompassed absolutely everything, motion and all, except solely for the red buffer beams.
Numerals on the T & D locos were cast plates while on the T & D, pale yellow painted numerals while on the C & L.