The red, black, and green colors indicate high, intermediate, and low activity levels for Drosophila genes that are regulated with a circadian rhythm. Patterns were revealed by hybridization of RNA samples, collected every four hours for six days, to DNA microarrays (each box shows a gene's response to one RNA sample with time read left to right). Each row shows all 36 responses of a single gene. Genes were ordered from top to bottom according to time of peak activity."