The black string is chosen for its strength and durability - invisible magician's thread is too weak and will break with active use. We tried using white, silver, and grey string and fishing line, and surprisingly they are more visible than black as they catch and reflect light. The flow-wand is not designed specifically for magic, but rather for movement. The magic is in your movement :)
If you prefer a nearly invisible string, you can search for invisible magician's thread online or try different options from your local fabric store, though you might find these are less durable.
You can find flow-wand string packs on our website here: http://www.flowtoys.com/flow-wand-string/
If you have any questions, please feel free to contact us!