Web Design in a Nutshell, 3rd Edition

Inline and background colors on 16-bit monitors

Often, you’ll want a graphic in the foreground to blend seamlessly with the background HTML color or a background graphic. As mentioned earlier, this is problematic on 16-bit monitors, because all RGB colors need to be remapped to the available 16-bit color space. Unfortunately, the same RGB value may be shifted in different directions depending on whether it appears as an inline graphic or a background graphic. The result is that you can see the rectangular edges of the graphic standing out against the background color. This is possible even if the same image file is used in the foreground and background. The outlines may be subtle, or they may be glaring. It’s unpredictable and unavoidable.

The solution for avoiding mismatched colors is to make the inline graphic a transparent GIF or PNG. That way, the background color merely shows through the edges of the graphic, and the rectangle is gone.