The test looked fair to me. They took two long tubes of equal lengths, filled one with distilled H2O and the other with distilled D2O. Then they looked at a white paper through both of them. The chemical properties of both liquids are different, and the paper looked blueish when looked through the H2O filled tube, but still looked white when looked through the D2) filled tube. That proved that H2O is a slightly blueish liquid, but D2O truly is colorless. If the tube was longer, the difference in colors would have been more noticeable. If there was only a small amount of liquid in each tube, the difference in the colors would have been so small, it would be hard to notice, which is why you never can tell this with just a glasss of water. What's unfair about the test, other than the fact that it shatters the previously held notion that water (in the form of H2O at least) is really a totally colorless liquid.
