The grey used by the GSR was as close to LMS grey as anything, though prior to that the GSWR used an extremely dark grey, almost black. CIE continued this shade to the late 50s / early 60s, then used a much lighter shade as shown on that open wagon above and on numerous "H" vans in the 60s and still like that in the 70s.
The brown used from the late 60s onwards always had a slight reddish tint, though this has been much more marked since the 1990s, as witnessed on Taras, timber wagons and container flats nowadays. In the 70s it was close enough to British Railways wagon brown.
Again, bear in mind that unlike BR wagons, Irish ones never had black chassis, always body colour; grey for grey wagons, brown for brown ones.
Exceptions to that rule were Asahi wagons, ammonia tanks, flat sided cement wagons of both types (blue chassis like bodies), bubbles (originally all over grey, then orange with black chassis, finally Irish Cement cream with - eh - cement coloured chassis!, and modern products of Limerick - brown bodies / chassis with black bogies, springs in all sorts of multi colours.
But for good old 4 wheel stock, see above.