A two dimensional cross-section of the three dimensional colloidal crystal. The crystal orientation in the upper part of the image is different from the lower part. A grain boundary separates these two sections of crystal. The circles represent the position of each spherical particle, and the central color of each circle represents the degree of positional fluctuation of each colloidal particle. Violet (red) represents the most (least) particle movement. Credit: Arjun Yodh, Penn State