Grey hair is read as wisdom, experience and the passage of time. Finding a single grey hair is usually taken as a first awareness that something in life is maturing or changing. Going grey all at once in a dream points to sudden worry, or to the weight of responsibilities that ages a person from the inside. Seeing a loved one with grey hair can reflect respect for them, or concern for how much they carry. Dream books also read it kindly, as a quiet acceptance of who you are becoming.
Where in your waking life have you met something like this lately?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.