The green and red coloured upholstery (1st & 2nd class) mentioned in the 1960s had disappeared by, at a wild guess, about 1970/2.
The dark charcoal grey with blue fleck became almost universal, though the Loughrea coach had light brown plastic “leather”, and I seem to recall some old laminates with light greyish blue, like Dublin buses.
It’s important to note that NONE of the RPSI or DCDR carriages have upholstery which is like the original. A few are roughly similar, but most including those shown above are completely different, with even base colours as different as painting a model ICR in NCC maroon with yellow wheels and a tartan roof!