Complexity and Diversity Complex organisms must produce and maintain an extraordinary diversity of cell and tissue types with a limited number of genes and molecular pathways. Cells accomplish this by reusing the same signaling networks at different times, in different tissues, and for different purposes, yet how this context-specificity is achieved is poorly understood. Jukam et al. ( 1238016 , published online 29 August) show how a set of genes that function in cell and tissue growth can be used again in nondividing fly photoreceptor neurons to ensure that flies develop appropriate sensitivity to both blue and green light. The Hippo pathway undergoes a regulatory change—from negative to positive feedback—that requires a tissue-specific transcription factor network. This network uses evolutionarily conserved regulatory factors whose mutations in humans result in degenerative retinal diseases. The context-appropriate positive feedback in flies ensures an all-or-nothing fate decision necessary to establish a functional visual system.