Belgium

The national flag of Belgium contains three equal vertical bands of black (hoist side), yellow, and red; the vertical design was based on the flag of France, whereas the colours were taken from the colours of the Duchy of Brabant.

When riots were starting as result of the Belgian revolution against the Dutch domination, a civil guard was established which wore the colours of Brabant. Its unusual proportions (13:15) are of unknown origin. [More info]
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