It's black when it's not in use, it's red when it's in use, and it's grey when you're done using it. What can this be??
The answer is Coal or charcoal.
EXPLANATION
t's black when it's not in use -> Coal or charcoal is initially black in color.
It's red when it's in use -> Coal/charcoal becomes red when heated (in use)
It's grey when you're done using it -> Coal/charcoal reduces to grey dust when spent or burnt off.
Edited on February 22, 2022, 2:03 am
Puzzle Solution
