What is black when you buy it red when you use it and gray when you throw it away?

Answer 1

Coal. Though many people think "charcoal" is the answer. Charcoal isn't red when you're using it nor grey when you throw it away. Coal and charcoal are entirely different.

Coal is red when it's aglow, grey as ash when it's thrown away.

Answer 2

coal you buy it black it burns red and then you throw it away gray as ash

Answer 3

Coal.