The perfect blackness indicates the purity of the evil within you.
Even if your eyes are weirdly colored, there is still a possibility of human connection, but if his/her eyes are gaping wells of nothingness..., you are no longer a human being.
To be a pure evil, you have to make your eyes completely black.
Only black sclera contacts can help you to have this effect.
In wearing black sclera contacts, your eyes will go perfect blackness, and your connection of human being will lost.
The key to be an evil, only with black sclera contacts