[2] It is the iron in hemoglobin specifically that gives blood its red colour.

The actual colour ranges from crimson to a dark brown-blood depending on how oxygenated the blood is, and may have a slightly orange hue.

Deoxygenated blood, which circulates closer to the body's surface and which is therefore generally more likely to be seen than oxygenated blood, issues from bodily veins in a dark red state, but quickly oxygenates upon exposure to air, turning a brighter shade of red.

[3] Arterial blood, which is already oxygenated, is also already a brighter shade of red— this is the blood seen from a pulsating neck, arm, or leg wound, and it does not change colour upon exposure to air.

In the RGB colour spectrum blood red often consists only of the colour red, with no green or blue component; in the CYMK colour model blood red has no cyan, and consists only of magenta and yellow with a small amount of black.