What's black when you buy it, red when you use it, and gray when you're done with it?

Charcoal.

Did You Know?

This riddle plays on charcoal's color transformation through its lifecycle — it starts black in the bag, glows red-hot when burning, and turns gray ash when spent! Charcoal has been used for cooking for thousands of years, with evidence dating back to ancient civilizations. Modern briquettes were invented in the 1920s by Henry Ford, who repurposed wood scraps from his car factories into the perfect backyard grilling fuel.