In this paper, we investigate the efficiency droop phenomenon in green and blue GaN-based micro-LEDs of various sizes. We discuss the distinct carrier overflow performance in green and blue devices by examining the doping profile extracted from capacitance-voltage characterization. By combining the size-dependent external quantum efficiency with the ABC model, we demonstrate the injection current efficiency droop. Furthermore, we observe that the efficiency droop is induced by injection current efficiency droop, with green micro-LEDs exhibiting a more pronounced droop due to more severe carrier overflow compared to blue micro-LEDs.