Basic Trope: A character finds a silver strand amongst his or her otherwise colored hairs and immediately feels old.
Straight: Alice finds a single gray hair and complains to her friends about how she is getting old.
Bob, 26, finds a single gray hair and acts as if his death is imminent.
Bob, 26, finds his whole head has turned gray overnight, perhaps from extreme fear or sorrow.
Downplayed: Alice notices her first gray hair in the mirror and frowns.
Justified: Bob has a "family curse" where a man always dies a week after finding a gray hair.
Inverted: Daniel has lived a long life and has a full head of silvers to show for it. But then he finds that he has a single strand of brown hair amongst them, making him feel younger than he has in years.
Alice finds a gray hair but just shrugs and goes on with her day.
Claire, who is known for her vanity, is combing her beautiful brown hair one day and finds some silver in there. She notes how starkly pretty it looks contrasted with her darker brown hair.
Bob looks in the mirror and finds a grey hair, to his surprise. But then he smiles - it turns out that he's happy to look more mature and experienced.
Bob looks in the mirror and finds a grey hair, but it just turns out to be his cat's hair. (His cat likes to sleep on his head at night.)
Elaine is brushing her hair and finds a gray hair in her brush after she's done, but then it turns out that her mom borrowed it without cleaning it out.
And then Alice thinks some more about her having found gray hair and freaks out because it means she's getting old(er) and that later will come wrinkles.
David removes the cat hair, and the real gray hair is underneath.
Elaine cleans out the brush and decides to move on with styling her hair. As she pulls it back, some gray hairs are revealed.
The entire plot revolves around multiple people finding gray hairs and all having Heroic BSODs over the revelations that they are getting old.
The gray hair is three feet longer than all her other hairs.
Zig Zagged: Elaine found some strands of silver hair on her hairbrush - later revealed to belong to her mother. When pulling back her hair, she saw that she really does have gray hairs. Until she remembered it was caused by some gray paint she used earlier.
Unexpectedly for someone of his age, Bob never finds any gray hairs at all.
Bob has found a gray hair one of many times and doesn't think much of it at all.
Alice is visibly acquiring more silver in her sable and she thinks it is beautiful rather than automatically synonymous with getting old
Enforced: Alice's actor was getting older and her character was getting played out. This plot was used to cause a shift in character.
Lampshaded: "Um, Sally, aren't you overreacting a bit?"
Invoked: Daniel knows how much Alice values her naturally youthful appearance, so to play a prank on her, he sneaks up on her while she sleeps and selectively dyes one or more strands of hair to make them apparently silver.
Exploited: Daniel knows how much Alice values her naturally youthful appearance, so when he hears about her freaking out over the gray hair, he starts running an anti-aging medical scam on her.
Defied: Bob refuses to make a big deal about the one gray hair he found that morning
Discussed: "Man, Bob's been really down since he found his first gray hair this morning."
Conversed: "How come whenever a character finds a gray hair, they always freak out about getting old?"
Deconstructed: Alice finds a gray hair and this makes her feel old, but she says nothing about it and starts plucking her silvers as she finds them
Reconstructed: Alice complains to her friends about her feeling old because she discovered gray hairs, the change in her hair care routine besides.
Played For Laughs: Carlos finds a gray hair and declares himself to be having a midlife crisis, leading him to do one or more ridiculously hilarious things to cheer himself up.
Played For Drama: Bob is genetically engineered. He was supposed to live until he lost his telomeres. This becomes the first sign that things are very wrong.