In contemporary popular culture green is the colour associated with being Irish and all things Irish. Historically however the Irish colour was blue, or St Patrick’s Blue. This is the ground colour of the arms of Ireland, of the Order of St Patrick, of the hackle of the Irish Guards in the Anglo-Irish tradition, and of the ground colour of flags in the past in the Nationalist one, and was used in all manner of uniforms and liveries. It is perhaps not surprising that its origins are a subject of serious debate, reflecting no doubt different Irish cultural traditions.
This use of a shade or shades of blue thus links with both of my previous posts for today. Wikipedia has a good illustrated article about the Irish emblematic use of the colour at St. Patrick's blue