Percutaneous extracorporeal circulation therapies such as apheresis and hemodialysis are commonly used in intensive care units, hemodialysis centers, and clinically settings. In these treatments, there is always a possibility of continuous bleeding from the puncture site. Since the blood flow in these therapies is high, a hemorrhagic shock may be caused by severe blood loss, and – in the worst case – this may even lead to the patient’s death. Therefore, it is important to continuously monitor blood leakage during the treatment. Typical procedures include the electrode method and the blood absorbance method, but their function may be affected by leakage of colored chemicals used, or by sweat or light. In this study, we developed a blood leakage determination module based on the chromaticity of a color sensor. Since the method is specifically sensitive to the red color, it can detect blood leakage. We performed experiments to verify the effectiveness of the proposed method and compared this new procedure with the existing ones, and we confirmed that the proposed method correctly detected blood leakage. Moreover, we investigated the blood detection capability of our new procedure and found that it could be applied to detect hematocrit levels within the range of 2% to 64%. We developed a multicolor sensor module and established a blood leakage detection method to meet the conditions that we had set as our goal. Our study confirmed that the proposed method did not cause malfunction due to leakage of chemical or presence of obstacle in the light path, while the traditional methods did. We also evaluated its performance and found that our method was able to detect blood leakage within the hematocrit range of 2% to 64%.