Yellow stains on otherwise silver or white hair can be the result of using the wrong shampoo, side effects from some medications, smoking, or a myriad of other causes. This page has advice for removing yellow stains from white hair.
Homemade Hair Dye Recipes
Bleaching Yellow From White Hair
Solutions for Over Processed Hair
Remedies for Hair Damaged by Perm
Using Leftover Hair Dye?
Caring For Long Hair