What likely happened was the lab tech ran a test for creatinine and specific gravity and found the levels being too low - hence the "diluted" ruling. Such tests are virtually SOP these days, making urine color the least aspect in determining an overly-diluted sample. Even samples with a nice yellow color to them can still register unsatisfactory in the creatinine and S/G department.

If your retest is indeed tomorrow morning, it would be too late for you to do any creatine-loading because it takes 2-3 days for the body to convert the creatine into creatinine in order for it to be present in the urine. Any creatine-loading must be done at least 3 days prior to the scheduled U/A.

Keep in mind that water is not the only fluid that can cause dilution. Any fluid consumed - including juices - can send the creatinine levels into a downward spiral and send up the red flags at the lab.