Question

explain why shadows are always black in colour

Answer 1

Opaque objects cast black shadows. This is because they block all light. Objects which block only some of the light can cast colored shadows. For example, an object that blocks only blue light will give a yellow shadow (as it lets red and green pass through) under a suitable light source.

Answer 2

shadow is create when there is any obticle in the way of the light ..

so when opticle stop the light it create a shadow. no light reach to it so it appear black