Step aside William and Kate, here's the real party.
But why all the orange? What's that got to do with the Dutch Queen?
First a bit of history. The progenitor of the Dutch Royal family is William, count of Orange. William received the title 'count of Orange' way back in the 8th century AC when he conquered the city of Orange in the south of France. That's why the Dutch royal family is named 'House of Orange'.
The Dutch flag is red, white and blue. But in the olden days it used to be orange, white and blue. Orange was only replaced by red in the last century. However, we still have a 'wimple' which is an orange extra on the flag, which makes the Dutch flag quite unique.
In 1885 politicians invented "princess's day', to celebrate the fifth birthday of princess Wilhelmina and to invoke a feeling of national unity. When Wilhelmina became queen, the yearly princess's day became queensday. When she was succeeded by her daughter Juliana, Queensday moved to the 30th of april, Juliana's birthday. In 1980 Juliana retired and the current queen Beatrix succeeded her. In honor of her mum, Beatrix kept queensday on the 30th of april.
Queensday is a national holiday. Tradionally, open-air parties are organized in all towns and villages, with artist's performances and music. Another tradition is that everyone can sell anything anywhere that day. This gave way to the world's largest garage sale. On queensday many people in Holland drag all the stuff they don't need anymore out into the streets to sell it. For 12 hours or so, a crazy buy and sell frenzy takes place, with people dancing in-between.
For most people these days, queensday is just an excuse for the biggest party of the year and doing crazy things with everything orange.
BTW, the Dutch national sports teams are always dressed in orange. Now you know why...