This is a very old term that is now carefully controlled by the FTC because of misuse and scams in the past. The dealer will probably tell you that it is a better diamond, but actually it is just the opposite. Blue-white refers to the fluorescence that results in natural light, which contains ultraviolet wavelengths. This blue fluorescence actually makes a colorless diamond look a little oily or milky in sunlight and decreases its value. However, for stones with a faint yellow color, a moderate amount of fluorescence can make it look whiter because it cancels some of the yellow.
Solution: Avoid any jeweler who still uses this term and walk out, since he may have old habits established by scam artists of the past.