The color comes mainly from bilirubin, a pigment that arises from the breakdown of red blood cells in the liver and bone marrow.
But the colour itself comes from iron. Iron in hemoglobin in red blood cells gives blood its red colour, and iron in the waste product bilirubin gives rise to its brown colour.
You're poo is always this colour because of the iron in you're body.
That's why it is always tha brown because when Iron passes through you're body it automatically turns brown! Hope this Helps xxxx