Why is blood flowing from lungs to the heartbrught red in color instead of dark red?

Blood flowing from the lungs to the heart is bright red because it is oxygenated. When blood passes through the lungs, it picks up oxygen, which binds to hemoglobin in red blood cells, causing the blood to appear bright red. In contrast, deoxygenated blood returning from the body to the heart is darker due to the lack of oxygen. This difference in color is primarily due to the chemical state of hemoglobin and its interaction with oxygen.