Riddle: what is described here?

[starlight]

It's black when you buy it, red when you use it, and grey when you throw it away. What is it?

 

[Darth Hendrix]

An african slave circa 1000bc?

 

[Brian]

ya they are right, its coal, and charcoal is not the answer i just had a barbe que and it just stays grey

 

[The Saint]

Coal or BBQ fuel, lol...!

 

[Kelli]

a newspaper?

edit: ah, coal's a good one. dern

 

[shego1142]

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.