Vanceday is a celebration that is observed all over the world. It is thought to be the main day in which tortured spirits return to seek vengeance. Because of this, people are expected to welcome them in a kind manor to show that they don't mean them harm. This is done by decorating with the specified colors, leaving offerings on their doorstep, dancing, etc.
The holiday itself was created by a man named Allion Vance who believed that his parents' souls would return on a specific day. He wished for people to welcome them and help them feel peace, so he had everyone in his village decorate with their favorite colors and leave offerings. He also wanted people to make them feel happy, so he had them dance and act merrily.
The people of his village enjoyed the holiday and it eventually spread throughout Astia and the world, becoming a worldwide holiday to welcome the spirits of the tortured.