A color diffusion transfer photographic film unit and a method for forming image therewith which comprises a photosensitive sheet comprising a light-reflective support having disposed thereon in order outwardly from the support (a) a layer having neutralizing function, (b) a dye image-receiving layer, (c) a separating layer and (d) at least one light-sensitive emulsion layer comprising a light-sensitive silver halide, the light-sensitive emulsion layer being associated with at least one dye image-forming material; a transparent cover sheet superposed on the outermost layer of the photosensitive sheet; and rupturable storage means for providing a developing solution substantially opaque to light between the light-sensitive emulsion layer and the transparent cover sheet; provided that at least one of the light-reflective support and layer thereon disposed on the side of the light-sensitive emulsion layer opposite the transparent cover sheet is substantially opaque to light.