Correct. The UTA painted some in a light grey, dark green and (bits of) red between the GNR takeover and the mid-60s; mostly on the Derry Road, plus a few on the NCC (Antrim and Ballymoney, in particular, surviving well into NIR times).
CIE, for their part, either left stations unpainted, as they had been in GNR days, on lines they had no future for, such as Oldcastle and the Dundalk - Clones - Cavan section. In other cases, they got the then-standard scheme of green (their green) and cream if repainted between 1958 and the very early 60s, but after the modernisation plan from the mid-60s they got the quite attractive and generally well-kept scheme which many of us will recall, of several shades of grey, white and black.
I'm guessing, by the green, that this one might possibly be CIE.......... but who's to say it's not faded UTA!
As always, this will be a fascinating thread as the story unfolds.