I am white when I am dirty, and black when I am clean. What am I?
A blackboard, black shirt? lots of possible answers
The answer was a blackboard.
You are a chalkboard.
Not a chalkboard. A blackboard.
Right. A chalkboard can be green. In fact,
I've seen more green ones than black ones.
I think your right.
Most chalkboard's are green though. The question says that it is black when it is clean.