What Makes The Colour Of Blood Red ?

Blood is red because of the number of red cells which exist in each drop of blood, far outweighing the white cells.  The cells are red because this is the inherent colour of the cell, resulting from its genetic and structural make up.

This begs the question, why red?  Well, whether evolution or God created mankind, the use of red for blood is possibly the best colour that could have been chosen.  Red is a colour which is very bright and distinguishable from other colours.  Thus it is always easy to know that we are bleeding.  Whatever the colour of our skin, blood is always highly visible, so it acts as a means of telling us to stop whatever we are doing and attend to the blood flow (i.e. try to stop it).  If blood were white or very pale, it is possible that we wouldn't immediately be able to tell that we were bleeding and could incur serious blood loss before we tended to the wound.  With bright red blood pouring out of us we cannot help but fail to notice it.