you do not want to ever soak a snake when its blue. That blue dullness is actually a layer of oil and fluid building up and separating the new layer of skin from the old layer of skin. Soaking the snake will leech that fluid out and almost guarantee you a bad shed.
Soak a snake after it has started shedding and is obviously not going to be able to finish its shed without assistance.
This is vitally important if there is a circular piece of shed constricting the snake anywhere along its body (neck, midsection, tail) because the shed will tighten and can cut off circulation.