In 1937 the Dutch flag was established by Queen Wilhelmina by means of a Royal Decree, which describes the three colours of the flag: bright vermilion (red), white and cobalt blue.
Dutch law does not set down any rules for the use of the Dutch flag. Anyone is permitted to fly the flag any day of the year. There are, however, rules for how the flag should be flown at government buildings, which can be found in the flag instructions.
There are customs and rules (protocol) associated with how the flag should be flown. For example, a hoisted flag should never touch the ground or obstruct traffic. It is also not customary to fly the flag between sunset and sunrise. If the flag is left out at night, it is regarded as good practice to illuminate the flag, so that the colours can clearly be seen.
History
The first reference to the Dutch flag dates from 1572. Its colours at that time were orange, white and blue. During the 17th century the orange was gradually replaced by red. It is said that this was because orange is less visible at sea than red.
The white and the blue came from the livery of the principality of Orange, while the orange evoked the principality more directly. After the French invasion in the late 18th century, the red, white and blue flag continued to be used, but the red band was embellished with the figure of a Dutch maiden with a lion at her feet. In one hand she bore a shield with the Roman fasces (a bundle of rods) and in the other, a lance crowned with the cap of liberty. King Louis Napoleon (reigned 1806-1810) abolished the image of the maiden and restored the old tricolour.
After the Netherlands was annexed by France in 1810, the national flag was replaced by the French imperial standard. In 1813 the Netherlands regained its independence and the House of Orange returned. At that time the colours of the flag were not officially established, meaning that both the red, white and blue version and the orange, white and blue version could be used. There was however a preference for the red, white and blue flag, and that was the one flown at government buildings. It was also around this time that it became customary to attach an orange pennon on special occasions associated with the Royal House.