The actual color of human blood is red. Blood is red due to the presence of a pigment called hemoglobin, which is found in red blood cells. Hemoglobin is responsible for carrying oxygen from the lungs to the body’s tissues and returning carbon dioxide, a waste product, from the tissues to the lungs for exhalation.
When blood is oxygenated (carrying oxygen), such as in the arteries, it appears bright red. This oxygenated blood is on its way to supply oxygen to the body’s tissues. In contrast, when blood is deoxygenated (having delivered oxygen to the tissues and returning to the heart through the veins), it appears darker red. The color change between oxygenated and deoxygenated blood is due to the oxygen content and the way that hemoglobin interacts with oxygen.
Blood is always some shade of red, either bright red when oxygen-rich or darker red when oxygen-depleted. The misconception that blood is blue inside the body is not accurate; it is a misunderstanding related to the way veins may appear under the skin, which can sometimes give the impression of a bluish or greenish color due to the way light interacts with tissues and skin.