Gray or white hair, which contains little or no pigment, sometimes gets yellow because it picks up pigments from the environment; for example, if you use a yellowish shampoo or conditioner, rather than a clear one, a trace of the color might be deposited on your hair. Chlorine and other chemical residues in water, sunlight, and even oils from the scalp can also give gray or white hair a yellowish cast. So if your water is very chlorinated, install a water filter in your shower; wear a hat when you're in the sun; and be sure to wash your hair regularly. Try products made specifically for gray hair, like Framesi Color Lover Shampoo for Grey Hair or Tressa Watercolors - Violet Wash.
Keep in mind: Adding a few silvery highlights can mean the difference between dull and dramatic.