I store the colored sand in plastic containers with lids when we are not using them. It is one of those less is more things. You really don't need a whole lot of sand in the container. It is fairly non-messy unless someone dumps the container.
The two year old has white sand with colored paper underneath. This is also a fun way to practice. The color shows through when they write. I think this is right before we had a little mess, but if you have two kids you know the youngest always wants to do what the oldest is doing. So I try to let him participate even if it means a possible mess.
Want to give it a try? You can get colored sand at most stores in the craft section, but if you don't get out much like me you can get some here on Amazon.
Have a great day!