Why did you become Caiqi Yang on the seventh day of burial?

This is a folk custom in some places. After death, it takes four sevens or ten sevens to form a seven. In case of the seventh, seventeenth and twenty-seventh day of the seventh lunar month, a small triangular colored flag will be made around the grave to show cracks; Danger, disaster, good for family, good for the dead, good for feng shui, and so on.