What am I?

I am black when clean and white when dirty. What am I?

related riddles

I have a tongue, but cannot speak. I have a bed but cannot sleep. I have four legs but cannot walk. Yet I move as you do. What am I?

First you see me in the grass dressed in yellow gay; next I am in dainty white, then I fly away. What am I?

I am a important part of your body.