The uniform of na Fianna has changed throughout the organisation’s 110+ year history. The Fianna Handbook is perhaps the best place to look at what the official uniform was at various times.
The 1914 edition states: “There are two Fianna uniforms, either of which can be selected by a sluagh, but all the boys in one sluagh should have the same. The uniforms are: Green slouch hat; olive green shirt (double-breasted, brass buttons, no pockets on outside of shirt, shoulder straps); dark breeches and putties or kilts with saffron “brat” caught at left shoulder with brooch.”
By 1964, when the third edition of the Fianna Handbook was published the uniform varied by rank as shown here:
Throughout the 1970s and 1980s the uniform would change. Here is a photo of Fianna in uniform meeting with veteran Republican Sighle Humphreys in 1982:
By the late 1980s, the 4th edition of the Fianna Handbook, published by the Provisional aligned Fianna, described their uniform as: “Green beret with Fianna badge, orange neckerchief, beige shirt, white lanyard, green jumper (winter only), black trousers/skirt, Fianna flash, and sam brown belt.”
This change in uniform was commented on by [the RSF-aligned] Fianna Éireann: “There exists at the moment a group of scouts styling themselves Na Fianna Éireann. They support this departure [SF taking seats in Leinster House] and have changed the green shirt of Na Fianna for the semi-khaki of England.”
By the late 1990s/early 2000s the current Fianna Éireann uniform was in place. It consists of an olive green military jumper, black trousers, black boots, black (and more recently green) beret with Fianna badge, green shirt (white in early 2000s), and sunglasses. Fianna óga wear an orange neckerchief. Different color epaulets signify rank.