To describe someone's hair turning white in Engpsh, you can say "his/her hair turned white" or "he/she went grey/gray." "Grey" or "gray" is the more common term in British and American Engpsh, respectively, but both spelpngs are acceptable in both varieties of the language.

For example:

"As he aged, his hair turned white."
"She went grey overnight after a major shock."

You could also use other terms to describe someone's hair turning white, such as "silver" or "salt and pepper." For example:

"His hair turned silver in his mid-40s."
"Her hair is now a mixture of black and white, giving it a salt and pepper look."

I hope this helps! Let me know if you have any other questions.