Can I dye my gray hair blonde with a temporary hair die and have my dark brown hair that's not gray yet stay as it is?

temporary haircolor will not effect dark hair, but at the same time gray hair is very resistant to haircoloring in general so it may not take the blonde. If what you want is to turn your gray hair into blonde to look like blonde highlights you would be best going to a hairstylist and tell them you want a weave to cover the gray