What’s with the Name?

Quite simply the name Orange derives from the orange fruit, whose name itself comes from the Sanskrit word nāraṅgaḥ or "orange tree". Transliterated into Latin as arangia it became orenge it Old French. The region of France known as Orange was named Arausio by the Romans:

"Arausio was a local Celtic water god who gave his name to the town of Arausio (Orange) in southern Gaul. Inscriptions attest to the presence of this presiding deity who gave the town its name."

The Roman and French names were conflated so the region became known as Orange.

The Principality of Orange (Principauté d'Orange) was established by the Holy Roman Emperor Frederick I in 1163 as an independent state under the house of Orange-Nassau. As part of the territory of the Dutch Republic the principality came under the auspices of William III.

Orange Protestants?

The colour orange has been associated with the majority of Irish Protestants since the 17th century after they sided with King William III of England, the Dutch Prince of Orange, won victory at the Battle of the Boyne in 1690 against King James II.

Williams’s victory secured the success of the "Glorious Revolution" of 1688-89 and its introduction of limited freedoms contained within the Bill of Rights; a move away from the absolutism advocated by King Louis XIV of France and his ally the deposed James II of England. Constitutional monarchy and modern democracy owes much to Williams European campaign against Louis XIV.

King Williams’s victory secured the temporary liberty of all Irish Protestants; however those of non-conformist denominations such as Presbyterians suffered persecution alongside Irish Catholics under the tyrannical Penal Laws.