help - how can i color platinum/gray hair to blond

Yes.  Grey hair does turn blonde when bleached. It may not do so evenly, so a toner may be required to get the desired color afterwards. Grey hair is very difficult to color with actual tint because it lacks some of the qualities of hair that still has pigment. The hair does not respond as well to the types of dyes used on hair with more pigment, as those need the pigment molecules within the hair to bind to. They do make tints specifically designed for grey and other hard to color types of hair, but they don't always perform as well as hoped.