Under certain circumstances you might use the same background color for your
legend background that you use in the map element to ensure that the colors will
look the same in the legend as they do on the map. For example, let’s say you have a
map with some buoy locations shown in yellow on top of blue water. For the map’s
legend, though, you’ve chosen a light‑yellow, almost tan, background color. If you try
to superimpose the buoy color onto this light‑yellow legend background, you’ll see
that the buoy color doesn’t look nearly as vibrant as it does on the blue water back‑
ground. It may even look like a different color entirely (see Figure 3.8). If you find
this sort of thing happening on one of your maps, the best thing to do is to change
the background color of the legend to something that more closely matches the main
background color of the map. This particular effect is called a “chromatic contrast.”
The same thing can happen with grayscale colors — called “achromatic contrast” or
“lightness contrast.”