What Is Black When You Buy It, Red When You Use It...

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

Answer: Charcoal.

Source: https://www.riddles.com/6

What is black when you buy it, red when you use it, and gray when you throw it away? — What is black when you buy it, red when you use it... by Anonymous v1.

Riddle: What is black when you buy it, red when you use it, and gray when you throw it away? Answer: Charcoal. — by Anonymous v2.