friends plz ans this question 
as penguin is most black then how can it camaflage only its belly is white ?

Black colour of Penguin helps in absorption of heat & provides it protection from predators also. Penguins blend with the darkness of ocean and hence cannot be viewed by the predators looking for them from above the ocean.
When they are at surface, white colour of their bellies help them to blend with the bright ocean surface and hence, they are protected from predators looking for them from below the ocean.
This type of camouflage shown by penguins is known as countershading.