The problem with coffe is not necessarily the diuretic effect or the caffeine it is that it is an acid producing agent in the stomach. When anything acid enters the stomach, it forces the body to use calcium, which is the bodies way of buffering the acid before it hits the blood stream. Since the blood always maintian a neutral PH, drinking coffee can cause you to deplete calium stores and everntually start leaching calcium from your bones to buffer the acid.
As far as the urine being clear, it only means that you are not pulling toxins with your water, it's not an indicator of hydration. Here is an experiment for you. Drink your normal water intake and watch your urine color. The next day, take a pinch of sea salt with each glass of water and watch your urine color. It will be dark and cloudy, which it should be to indicate that your kidneys are actually filtering your body, which is their job. Forcing them to process excess water with no salt, clear urine, is stressful and in the long run can cause adrenal exhaustion and kidney disease later in life becasue those toxins will accumualte in the kidneys. If you drink a lot of coffee, that disease will be kidney stones, which are calcium deposits. You must have salt, not table salt, but good clean salt, with your water so the kidneys function properly.