The colors of the Dutch flag are symbols: red stands for the people, white for the church and blue for the nobility.
The Dutch flag has its roots in 16th century when Willem van Oranje used it in the Dutch war of Independence. At that time the flag wasn’t red, white, blue but orange, white, blue. The orange referred to Willem’s last name: Oranje. Soon the orange changed to red because red is more visuable at sea, which is where the flag was mainly used.
At 1937 the red, white, blue flag was officially introduced by Queen Wilhelmina.