what does black cloth mean?

Black often indicates solemnity. It can indicate death, or mourning, or some significant change in life, like a graduation or a wedding.

Depends on what's been made out of the black cloth. Is it a tuxedo? A t-shirt? A business suit? A flag? A handkerchief?

A white cloth.

You mean symbolically? It depends on the context. Priests and nuns wear it for different reasons than judges and restaurant staff.