A white or grayish white substance can be formed by dipping, in the first step, aluminum or an aluminum alloy having an anodically oxidized film in a first solution containing a specific salt or electrolyzing with said first solution, thereby causing the product from this salt to enter into the micropore of said film and then, in the subsequent second step, dipping the product from the first step in a second solution containing a substance which reacts with the product from the salt to be converted into a white or grayish white compound or electrolyzing with said second solution.