that indicates wayyyyyyyyyy too much strain on the kidneys or kidney failure. or bleeding in the kidneys.
healthy urine should be from a light straw color (almost clear) to a dark yellow.
if your urine gets dark brown break your fast and go to the doctors and explain what you did before with 100% truth.
now if you are into your fast and your pee isnt colored at all and is clear this indicates liver strain. again a reason for breaking and going to the doctor.