Final answer:
Urine can appear red due to the consumption of certain foods, medical conditions like urinary system cancer or kidney stones, and diseases affecting the liver or bile ducts. Red urine can also be caused by the oxidation of porphobilinogen upon light exposure.
Step-by-step explanation:
Aside from blood, urine can appear red due to the consumption of certain foods, such as beets, berries, and fava beans, which can cause a harmless change in urine color. Moreover, the breakdown products of red blood cell destruction, namely urochrome, influence the normal yellow color of urine.
However, medical conditions like a urinary system cancer or a kidney stone, as well as diseases affecting the liver or bile ducts, can also alter urine color to red or dark "tea" or "cola" color. Dehydration also results in darker urine. Notably, in some instances, urine can be red due to the oxidation of porphobilinogen after exposure to light, which can be associated with various symptoms, including abdominal pain and cutaneous hypersensitivity to light.