The map in the previous post looked deceptively simple. It might give you the impression that such a design is easy to make. As it happens, today Wired.com obliged me by providing an example showing it's NOT that easy....
The map below was published on Wired to show the differences in prices of broadband internet access. Each color indicates a certain price in broadband access. Can you make sense of it? I can't. And my eyes start hurting when I try.

I won't comment on the graphic design, because I want to focus on the choice of colors. To illustrate that the quality of the map very much hinges on the choice of colors, I reworked the map in all new colors. See below.

First I made sure to have enough contrast between the background and the landmasses. So that at least you'll be able to see the different continents. Because I used black in the background, all the other colors have a brightness of at least 40%. See my post on contrasts for further explanation. Then I established a hierarchy of colors so that the cheaper the internet access, the lighter the color. Grey indicates where broadband is not available. I followed the natural brightness of the colors as explained here. It's a real simple color design. No big deal. But now the map does clearly indicate where in the world you have the best chance of finding cheap internet access. And as a bonus it's more pleasing to the eye as well....