The yellow color in urine is due to presence of urobilins. It is produced by the breakdown of the bile pigment bilirubin. Similarly, Bilirubin is produced from heme of hemoglobin. Most of the bilirubin is partly catabolised in liver and stored in gall bladder. It further breaks in intestines and excreted in the feces.  But some of the bilirubins remain in bloodstream which is extracted by the kidneys in the form of urobilins which gives yellow colour urine.