Any alteration, incidental alteration or minor work done to the street wall of any building or portion of any building shall be accomplished in such matter that:
(a) such street wall is treated with consistent materials, color and texture from the top of any ground floor windows or sign board to the top or the parapet, or to the bottom of a cornice if a cornice exists (access doors or panels, grilles or similar features shall be as inconspicuous as possible); and
(b) where such street wall treatment covers any window opening, it shall completely cover all window openings in the street wall; or
(c) where window openings remain uncovered, all windows shall be treated in a similar manner or, if sealed, all windows shall be covered by a panel set at least two inches behind the plane of the wall. Except where the material used to seal window openings is the same as the wall of the building, the window panel shall have a single color over its entire surface. All such window panels shall have the same color.