In 1572 the orange-white-blue flag was first mentioned when the town of Den Briel was liberated.
The red-white-blue flag was first mentioned in 1596.
Around 1630 more flags with a red stripe were used, and after 1660 the version with the orange stripe became very rare. It's still unknown why the orange stripe was changed to red, but there are two main theories:
1. a new method of producing orange paint resulted in a darker shade, almost red.
2. the House of Orange became less popular.
The colours were however never laid down officially, so in the 1930s the question of red versus orange was raised again, especially by the national socialist NSB party, who used the orange version. On 19 February 1937 Queen Wilhelmina decided by Order in council that: "The colours of the flag of the Kingdom of the Netherlands are red, white and blue." In 1958 the colours were defined more precisely as bright vermilion and cobalt blue.