These gels contain long-lived clusters or strands of nanoparticles that, locally, have a welldefined orientation with respect to the incident electric field polarization. It seems reasonable that colloidal fluids, which do not have long-lived assembled motifs, would not display welloriented collective resonant structures. Perhaps surprisingly, collective resonant structural features also occur in uniform colloidal fluids (Figure ). These features are now transient, changing with the diffusive motion of the particles but statistically identical at each time point. Though the overall configuration is isotropic (Figure and 9D), the low-frequency resonating red particles are aligned parallel to Ê0 (Figure ) and display a butterfly pattern in S(q) (Figure ). The large rise in S(q) at low |q| indicates that these particles are also found closer to one another than average. These features are qualitatively identical to those in gels (Figure and). The high-frequency resonating blue particles (Figure ), on the other hand, are found far from one another as indicated by the suppressed S(q) rise at low |q| (Figure ). In contrast the blue resonators in colloidal gels are, like all particles, found within dense clusters. The dense blue clusters give a well-defined orientation in the S(q) pattern for gels (Figure ), but the S(q) for colloidal fluids (Figure ) is mostly unstructured, showing only small deviations from 1.