The color of the blood in a human's veins is typically a dark red. This coloration is due to the deoxygenated hemoglobin present in the blood. When blood is rich in oxygen, as it travels from the lungs to the arteries, it appears bright red. However, as it circulates the body and releases oxygen to tissues, it becomes low in oxygen and takes on a darker hue. It's important to note that while the blood in veins looks dark red, it is not blue; the misconception arises from how the skin reflects light and the optical effects of tissue.