Generally the color of your urine is determined by how concentrated it is. The darker the color, the more concentrated your urine.
If you wait four hours and drink a bunch of water, your urine will be more dilute and thus lighter in color than if you had waited the same four hours and not consumed much liquids.
Excess and waste product hormones are filtered out of your body and into your bladder. The longer you wait, the higher the concentration of said hormones will be. However if you drink a lot of water, this lowers the concentration. It's like adding water to orange juice, if you imagine the orange flavor to be hCG. The more water you add to the orange juice, the less you can taste the orange flavor.
Does that make any sense?
