Abstract: A method for locally enhancing the contrast of a yellow image, which method comprises providing a yellow image on a white background, said image comprised of yellow areas and white areas, said yellow areas and white areas exhibiting pH levels which differ by at least 0.5 in an aqueous environment, applying to at least a portion of said yellow image a solution of a pH color changing dye which will change color to a color other than yellow when coated on one of said yellow areas or white areas and not change color when coated on the other of said yellow areas or white areas, thereby forming a colored image duplicating the yellow image in areas where the solution has been applied, said colored image having a visually better contrast than said yellow image.