When Marge makes her routine visit to the salon, she admits to finding a single gray hair. This prompts her stylist to give her the truth: that she's been "grayer than a Seattle Cinco de Mayo for years now."
What's worse is that the blue chemicals are so potent that they wipe the experience from her mind each time. After seeing a gray-haired (and happy!) couple, she decides to ditch the blue hair.
Her family hates it, and everyone else she runs into seems to be giving her compliments veiled with cruelty. She loses it when she's asked for her AARP card at the grocery store.
Marge seeks comfort in her sisters—who seem to have had gray hair for a long time now. Turns out, it's just cigarette ash.
While Marge is fighting an inner battle with her appearance, Homer is out helping his friends get ladies by playing the part of Wingman. Marge mistook this for his cheating on her, and when she confronts him at the club, he sorts it all out—and reveals a blue-headed "type." At the end of the episode, Marge goes back to blue.