•Signaling complexes have distinct assembly architectures and fundamentally change signaling dynamics within the cell.•The interactions between a complex's components can be monitored in real-time using optical methods such as FRET and BiFC.•Genetically encoded biosensors measure changes in biological activity and can be used to study signaling in situ. Protein complexes play a major role in transducing information from outside the cell into instructions for growth and survival, and understanding how these complexes relay and shape intracellular signals has been a central question in signaling biology. Fluorescent proteins have proven paramount in opening windows for researchers to peer into the architecture and inner workings of signaling assemblies within the living cell and in real-time. In this review, we will provide readers with a current perspective on the development and use of genetically encoded optical probes to dissect the function of signaling complexes.