The liquid that leaves the body is almost unrelated, in chemical composition, to the liquid consumed. Any substance, solid or liquid, that goes down the esophagus, passes through the digestive tract and, if not absorbed, is incorporated into the faecal matter. Urine, in contrast, is created by the kidneys from metabolic waste produced in the tissues and transported through the bloodstream. Any coloured compound that one drinks either will or will not interact biochemically with the body’s system. If it does, this interaction (like any other chemical reaction it might undergo) will tend to alter or eliminate its colour. If it does not, the digestive system will usually decline to absorb it and will be excerted in the faeces which, you will have noticed, show considerable colour variation than the urine.
Coloured substances in food and drink are usually organic compounds that the human body has an amazing ability to metabolize, turning them into colourless carbon dioxide, water and urea.
The toughest stuff is often taken care of by the liver, which is a veritable waste incinerator. However, on the very infrequent occasion when the intake of coloured substances exceeds what the body can quickly metabolize, the colour is not necessarily removed as the liquid leaves the body. This is well known to anyone who has indulged in large quantities of borsch, or the Russian beetroot soup.