The coffee ring effect is a phenomenon in which a ring-shaped pattern forms when droplets containing particles evaporate. This ring formation is caused by capillary flow during the drying process, and some particles remain irregularly distributed within the ring. When light is shone on these residual particles at an appropriate angle, this structure exhibits a unique color. In this study, we investigated the macroscopic and microscopic coloration phenomena of coffee rings formed by polystyrene beads (diameter 0.5–3 µm) and yeast cells. The macroscopic coloration was observed by spectral analysis, and the microscopic coloration was observed by optical microscopy. We also discussed the formation of speckle patterns by coffee rings formed by yeast cells. These results suggest that coffee rings formed by yeast cells function as optical elements, indicating the potential for utilizing microbial cells as optical elements in sensors, structural color devices, and other applications.