It depends on what you are looking for and where the tank is. If you are looking for your tank to act as a reading light, blue will brighten things up nicely outside the tank. If you want corals to look more colorful, black will bring out the color of the corals a little more. If you have your tank in a nice bright room or in a place where people will see it when they walk in your door, blue has a nice effect, but if the tank is in a room with darker colored walls or tucked away in your basement or family den black is the better option. I have mine painted black because the wall color is a blue-gray and is in a room with not so bright lighting.