Festival of the End and the Beginning

A tradition amongst Arcankin to celebrate the end of the Surging Age and the subsequent rebirth of their species. The festival takes place in the middle of the spring season lasting for five days. It is a custom to decorate using rainbows or colors on the rainbow, their variants included.
What does the rainbow symbolize in a culture of your world?
The rainbow becomes associated with the end of hardship, good fortune, and happiness. This symbolization applies to those that lived during in the Surging Age where life was rough and fleeting due to the arcane surges and natural disasters were a common occurrence. When the Surging Age came to an end, rainbows were visible seemingly leading to one location.

History

How did it begin?
The ending years of the Surging Age saw many acts of violence being perpetuated on top of the magical phenomena and natural disasters. While many thought nothing of it, things came to an end at the dawn of the Vengeance War. Many hesitate to call it a war as after a certain point wherein a light shone so brightly it caused a massive flux of rainbows on the reflection of armors and heralded a dragon that came to assist the one leading the charge against the civilizations. After this day, the battles casualties were higher as those wielding magic, now dubbing themselves the Arcankin, were increasing in power and those not wanting to die at the hands of the Arcankin would join them. In five days, the wars ended with the Arcankin being the victors.
Changes
Many changes happen to the festival after the first one that celebrated the end of the war. The biggest change being that the celebrations are extended from five days to seven days as cities were being built. Another change is the shift in focus from the end of the war to enjoying peace as over the decades the war would be farther and farther away. To compensate, days focusing on memorializing the war would happen in the later, more somber, seasons.