This is a lovely way for you to demonstrate your unity whilst creating a lasting memento of your special day. Each of you will have a small jar of coloured sand which you take turns to pour into a larger jar or vase, usually whilst saying promises to one another.
As each of you pour your sand in turn the colours build up creating layers and patterns until the jar is full. The jar is then sealed and the sand cannot be separated just as your bond cannot be separated.
The colours you choose are entirely up to you, it can be to match your colour scheme, if you have one, or it may just be your favourite colours