April is often associated with tulips, but the first of the month is associated with fools.
Here is an edited close up of the tulip flag from the painting Wagon of Fools by Hendrik Gerritsz Pot. Hendrik was from the original Harlem in the Netherlands.The April Fools Tulip Flag has a light blue background with a tulip bulb with four white tulips shoots.
In 1637, wild trade and speculation in fashionable and novel tulip futures led to one of the first modern economic bubbles. It was a memorable moment and this unfortunate aspect of 'free' economies was memorialized in the a contemporary painting.