Green may well reflect both his party and political background, but the Taoiseach has been immortalised in a colour of an altogether different hue.
Blue is the predominant background in the official State portrait of Mr Ahern, to be unveiled next week at the RHA's annual exhibition in Dublin.
However, anybody reading anything political into the choice of colour is mistaken, according to the artist, James Hanley, who said Mr Ahern had had no input on the background colour. "The blue background was influenced by the fact that he's a Dublin Taoiseach," according to the artist . The Taoiseach sat for the painting several times at the painter's studio, which is in Mr Ahern's constituency.
Mr Hanley (38) has emerged as one of the country's most prominent portraitists. Commissions have included a painting of the Irish Olympic gold medallist, Mr Ronnie Delany, for the National Gallery's collection, and the late Maureen Potter for the Gaiety Theatre. The artistic challenge of the piece, according to Mr Hanley, was to ensure it was not just another "man in a suit", by creating an image which concentrates the viewer's eye on the face.
He acknowledged that sitting for the portrait might have been somewhat uncomfortable for the Taoiseach, in that the work will not be hung in the Oireachtas until his political career is over and he has left the Dáil.
Any concerns he might have had are not evident now, said Mr Hanley. "He's very happy with the painting. It's been hanging in his office in Government Buildings since it was completed," he added.
Unusually for Mr Hanley's portraits, the painting does not include emblematic images associated with the sitter. This was vetoed by the Taoiseach, who was against putting political paraphernalia in the piece.
The painting will be one of 450 works which will be on display at the RHA's 174th exhibition at its gallery in Ely Place, Dublin, from next Tuesday. Entry is free.