The proper vitamin to use for color is B2 (Riboflavin). Bran Flakes cereals such as Total or Product 19 are rich in Riboflavin.

Bear in mind that creatinine and specific gravity checks have became the norm in recent years, rendering specimen color the least aspect in determining an overly-diluted sample. Even urine samples with a nice yellow color to them can still fall below the acceptable limits for creatinine and SG. Therefore, when doing dilution techniques, the focus should be on making sure the creatinine and SG are within acceptable limits. For tips, read up on the Dilution "sticky" thread.