Final answer:
Dark red colored blood, indicating low oxygen content, would be found in the venae cavae, traveling back to the right atrium.
Step-by-step explanation:
Dark red colored blood would be found in the inferior and superior venae cavae, traveling to the right atrium of the heart. This dark red color indicates that the blood has little oxygen bound to it, as it returns to the heart after circulating through the body. The hemoglobin within red blood cells is responsible for the transport of oxygen and gives blood its red color. Oxygenated blood is bright red and travels from the heart to the body, while deoxygenated blood loses its brightness, becoming darker as it carries less oxygen.
The systemic circulation set out in the diagrams and figures illustrates the dual nature of the human blood circulation, with oxygenated blood being pumped out of the left side of the heart through the aorta and deoxygenated blood returning to the right side via the venae cavae. The blood becomes oxygenated in the lungs through gas exchange before returning to the left atrium and exiting the heart again.