With a dash of magnetic dust
Our ferromagnetic "ferrodripper" is filled with a magnetic sand similar to that which you would find in an "etch-a-sketch". This medium-fine powder is not only sensitive to magnets, but also changes the flow patterns of the fluids when the dripper is flipped over or turned.
These work with regular household magnets, while neodymium earth magnets (available separately on amazon & other retailers) will produce an even stronger reaction.
Similar physics toys you're likely familiar with typically feature a back ferroliquid liquid suspended in a clear oil. After experimenting with different formulas we determined that flakes have a gnarlier appearance, and won't stain the plastic shells over time as this dark colored liquid is prone to do. Most importantly — by using this magnetic dust instead of a dark ferro-liquid — we are able to include up to four distinct colors in each dripper as opposed to just two if we were using a traditional ferrofluid.
To avoid scuffing the plastic surface we suggest you keep a small gap of air of a few millimeters or more between the magnet and the dripper.