The color of human blood inside the body is typically a shade of red, but it can vary depending on where it is in the circulatory system:
1. **Arterial Blood**: Blood that has just been oxygenated in the lungs and is leaving the heart through the arteries is bright red. This is because it is carrying oxygen-bound hemoglobin (oxyhemoglobin), which gives it a vibrant red color.
2. **Venous Blood**: Blood that has delivered oxygen to the body's tissues and is returning to the heart through the veins is darker in color. This is because it contains a higher proportion of deoxygenated hemoglobin (deoxyhemoglobin), which appears bluish-red.
So, while the blood is still inside the body, it appears red in arteries and darker, more bluish-red in veins. The difference in color is due to the oxygenation state of the hemoglobin in the red blood cells.