Re: Color of blood that is still inside the human body

What color is blood …really ?
Human blood is made up of a liquid part and a solid part.
The liquid part, when it is still in the body, is called plasma.
It is yellowish in color.  It makes up about 50 - 60 % of our blood.
The solid part is made up of cells; red blood cells, white blood cells
and  platelets.  

White blood cells and platelets have no color but appear white when they 
are grouped together, as when blood is separated in a centrifuge.  Together 
they make  up less than 1 % of the blood.  They are pictured in text books 
as having a variety of colors.  This is because they can be stained with 
various dyes after they are removed from the body then placed on a glass 
slide.

Red blood cells are always red.  Since RBCs make up about 40-45% of our 
blood, the blood is red.  Red blood cells are red because they have a 
protein called hemoglobin which  contains iron.  Iron likes to bind oxygen.  
Oxygen combined with iron is red.  The more oxygen iron has bound to 
it, the redder it is.

It is true that some persons have "iron poor blood".  In this case their 
red blood cells  are less red than normal, but they are still red.  The 
iron in the hemoglobin of red blood cells is what carries oxygen to every 
tissue in the body.

Why some people may think that blood can be blue is probably because of the
color of our veins, which may be visible near the skin's surface.  They 
appear blue because they do not get as much oxygen as the other tissues.  

When the red blood cells go to the lungs, the iron in them picks up oxygen. 
Blood then goes to the heart and then to the rest of the body through 
vessels called arteries.  The arteries appear reddish as do many other 
organs, because the iron in the blood gives up its oxygen to the cells that 
need it as the red blood cells travel throughout the body.  By the time the 
blood is back on its way to the heart and then to the lungs it has less 
than half as much oxygen as it did before.  The veins, therefore, do not 
get as much oxygen as the other tissues and they appear bluish.

The bottom line is: blood is red.