A horizontal triband of blue, white, blue. Centred on the white band, the Sun of May.
Juan Manuel de Rosas' rose to power on 6 December, 1829 to become Governor of Buenos Aires Province - effectively President - of the United Provinces of the Río de la Plata. Some time after his appointment, the flag was changed to the dark blue due to the association of the traditional light blue being associated with the Unitarians, the rival political group at the time.
On 4 January, 1831, the Federal Pact gave birth to the Argentine Confederation.