Apart from the two tone green, there doesn't appear to be any across the board livery used by both rail and bus.
The tour bus "banana boat" livery compliments the coachwork, together with the individual river names looks intentionally chosen to stand out from the sea of green buses, it was a favourite subject for publicity photos and at least one poster. Beyond some GM promotional material, the 121 in grey/yellow didn't get much of the publicity machine limelight for what was a brand new loco. The CIE bus red/white scheme may be a carry over from IOC days, perhaps the city services dark blue/cream was GNRI motor coach dept inspired.
As an aside, the grey/yellow 121 does make an appearance of a few seconds in the old Soviet Union-esque RTE National Anthem reel.