The color of urine normally ranges from colourless to yellow. The yellow color is caused by urobilins, which are produced by the breakdown of hemoglobin, the substance that gives blood its red color. If a person is dehydrated, less urine will be produced (maybe less than one liter per day), and it will be more concentrated. If a person drinks a lot of water, more urine will be produced (maybe as much as two liters per day) and it will be less concentrated.