Most of the time they will put blue in the toilet so that you can't dilute your urine with toilet water anyway, so they won't be able to tell what color your urine is. I have not seen or heard of a testing center that doesn't do that-but in case they don't you peeing in the toilet is like peeing in the ocean. They will not look to compare coloring because they won't be able to give a true reading. I know that like quick fix, each batch is a little different in coloring. I used to keep a couple on hand when I used to get randoms, and if memory serves I don't think I have ever had 2 that were the same color, and most are the really bright yellow.