If you are taking a multi vitamin containing B-vitamins, or are taking a B-complex, that can turn your urine a very bight neon yellow. But, I think this is different than what Moreless is talking about. If your urine is a dark yellow (going to the brown side of the scale, rather then the bright neon side, that is when there is a problem. Also, certain foods like beets will also color your urine.