Water by definition has no color. Pure water is transparent, a property which means that light can pass through it unimpeded. In order for a substance to have a color, it must reflect some wavelengths of light. When light is reflected off a substance back to your eyes, the reflected wavelengths enter the eyeball, hit the retina, and are interpreted into visual signals. If a substance reflects all the wavelengths that hit it, we see white. If a substance absorbs all the wavelengths, we see black, which is brain's interpretation of the absence of light. When a substance absorbs some wavelengths and reflects others, we see the colors that are reflected. For example, a blue shirt looks blue under white light because the shirt absorbs all the colors except blue, which is reflected back and enters your eyes.