Color works. It helps that in this case, the characteristic being mapped is eye color, so it’s kind of a no-brainer to shade the areas where blue eyes are prevalent in blue and the areas where brown eyes are prevalent in brown. Even if this graph were to be printed in a grayscale journal (which is probably why the one on the left tries to use hatching to distinguish the areas), using degrees of full shading is easier to distinguish than using hatching patterns. Most printers can handle printing 10% gray, 50% gray, and so on.
What Needs Work
The areas that need some work, even in the color version, are the areas between blue and brown. Right now, those areas are lighter blue and lighter brown. The problem is that because the blue is mapping directly to the characteristic in question – blue eyes, blue area – it’s easy to think that the lighter blue areas represent areas where people have really light blue eyes. But, in fact, those areas are full of a mix of people, some with light eyes, some with dark eyes. I might have gone with a staggered blue/brown pattern or just chosen a color that doesn’t have anything to do with eye color, like purple.
Peter Frost (2006) Why Do Europeans Have So Many Hair and Eye Colors?
Western Paradigm blog (February 2008) The Blue Eye Map of Europe [Note to Readers: I couldn’t find the original version of the color map so I am linking to the blog where I found it rather than the original source.]