A similar image with 16 shades of gray (four-bit color) may look very close to one with 256 shades of gray but the palette has less variations with which to work. The subtleties permit data to be stored without the human eye catching the changes. Many argue that gray-scale images render the "best" results for steganography. However, using gray- scale or color is not as important as the subtleties in color variation. Consider the following two 256 color palettes.
Figure 3 illustrates subtle changes in color variations. It is difficult to differentiate between many of the colors in this palette. Is this palette in Figure 2 "good" for steganography? Well, it depends. Subtle color changes can be seen in Figure 2, but other color variances seem to be rather drastic. However, one must consider the image in addition to the palette. Obviously, an image with large areas of solid colors is a poor choice as variances created from the embedded message will be noticeable in the solid areas (a palette as in Figure 3 would offset this). Figure 2 is the palette from a 256 color version of Renoir's Le Moulin de la Galette. Based on embedding this image with text and graphic messages, it is a very good container for holding data.