Black and White Issue

[whoose]

While riding the chair lift at our local ski hill yesterday a I told a friend about my water wall. He said good idea but you need to put something black behind the 1 gallon jugs. I know a little Physics and I said to him that the light has already passed through the water and would only be absorbed by the black background. I suggested white or shinny silver. He said no and suggested I watch some YouTube. Got to the top of the hill. Who is Correct and why?