In other words, they made a liquid than can change to any color desired, and with a huge amount of control and precision. The article has an excellent description of how this is done.
A research team headed by Yadong Yin at the University of California, Riverside(USA) has now shared the secret of their wonderful liquid with the journal Angewandte Chemie: Nanoscopic particles made of tiny magnetic crystals coated with a plastic shell self-assemble in solution to form photonic crystals—semiconductors for light. When a magnetic field is applied, the optical properties of the crystals change, allowing their color to be very precisely adjusted through variation of the strength of the field.
...This response is rapid and fully reversible because the nanocrystals in clusters are so small that they lose their magnetism when the magnetic field is shut off (superparamagnetism). Potential applications for these switchable “optical semiconductors” include novel optoelectronic components for telecommunications, displays, and sensors.
I wonder if they'll ever put this into clothing, or jewelry...
Citation: Yadong Yin, Highly Tunable Superparamagnetic Colloidal Photonic Crystals, Angewandte Chemie International Edition, doi: 10.1002/anie.200701992