His skinny form gets far more screen time than his hero version, but All Might’s civilian look has brought some confusion to his design. Why does All Might have black eyes?
All Might has black eyes because his skinny form is so gaunt that it creates a shadow on his face. Mangaka Kohei Horikoshi explained All Might’s design in the bonus page of the opening chapter.
The bonus page also featured a first draft design of All Might and other fun information about his creation. Deku and All Might were able to meet in chapter #1 and see his true form.
Horikoshi explains why All Might has black eyes
At the end of chapter #1, mangaka Kohei Horikoshi shared an early sketch of All Might in civilian clothes. The sketch states that All Might is 220cm, was born on June 10th, and his favorite things are Yakushima cedars and movies.
Under the header titled “The Supplement,” Horikoshi went into detail about All Might’s design.
Horikoshi explains that the whites of All Might’s eyes are all black when in his skinny form. All Might is so gaunt that his “black eyes” are perpetually in shadow. Also, his pupils glisten to “reflect the true strength and dignity of this ‘symbol of peace’.”
The mangaka wanted everything that All Might’s muscle form represents to be condensed into the pupils. Horikoshi writes in the explanation that he doesn’t consider himself a good enough artist to express that idea properly.
He goes into other details regarding All Might’s look. Horikoshi felt the initial design of All Might was cool, but a concern at an editorial department meeting was raised that All Might was too old and couldn’t be looked up to by audiences. The editors suggested more of a “pretty boy,” but Horikoshi says those criticisms fan the flames when he puts attention to drawing All Might.
So that’s the official answer. All Might has black eyes because his skinny form is so gaunt that it creates a shadow on his face.