In 1830, the flag, at that time non-officially, consisted of three horizontal bands, with the colors red, yellow and black.

On 23 January 1831, the National Congress enshrined the tricolor in the Constitution, but did not determine the direction and order of the color bands.

[1] The territory then passed into Spanish hands, and after the coronation of Charles V, Holy Roman Emperor, yellow and red, the colours of Spain, were added.

The population of Brussels was opposed to this, and, following the example of France, red, yellow and black cockades began to appear, those being the colours of Brabant.

[1] On 26 August 1830, the day after the rioting at the La Monnaie opera house and the start of the Belgian Revolution, the flag of France flew from the city hall of Brussels.

The insurgents hastily replaced it with a tricolour of red, yellow, and black horizontal stripes (similar to the one used during the Brabant Revolution[1] of 1789–1790 which had established the United States of Belgium) made at a nearby fabric store.

As a result, Article 193 of the Constitution of Belgium describes the colours of the Belgian nation as Red, Yellow, and Black, the reverse order shown in the official flag.

These proportions are explained as an aesthetic consideration, as the palaces are large, and the flags are thus viewed from far below, which makes them look more normal due to foreshortening.