The flowing sand and blending of the colors in the Unity Sand Ceremony symbolize the bringing together of two lives into one. The two sands symbolize everything that the bride and groom have been or will become in the future.
The blending of the sand represents the union not only of them but their friends and families as well. The separate sands once poured into the unity vase can never be put back into their separate vases. They are forever entwined just as the lives and loves of the bride and groom.
Some couples prefer to leave a small amount of sand in their respective container to show that even though they now function as one, they remain individuals.