The flag of Hungary (Hungarian: Magyarország zászlaja) is a horizontal tricolour of red, white and green. In this exact form, it has been the official flag of Hungary since 23 May 1957. The flag's form originates from national republican movements of the 18th and 19th centuries, while its colours are from the Middle Ages. The current Hungarian tricolour flag is the same as the republican movement flag of the United Kingdom (used since 1816) and the colours in that form were already used at least since the coronation of Leopold II in 1790, predating the first use of the Italian Tricolour in 1797.
Courtesy of Dédé11 from postcrossing forum