December 22, 2014

Red & Green Color Scales? Maybe for Christmas

  


Tis the season!

I’m as guilty as the next guy. When I first started out building data visualizations and dashboards I was quick to select a Red-Green color scale to differentiate between good and bad. In my defense, in the United States green is often associated with good results, red with bad results. Additionally, it didn’t help that many of the available tools defaulted to the red-green scale as the vendors weren’t focused on sound data visualization practices.

So what’s the drawback of using the red-green color scale?

First, color meaning varies greatly between cultures. i.e. Red typically  symbolizes “bad” in western cultures…in China red symbolizes good luck, happiness and long life…all positives. As for green, western cultures often associate green with “good”, whereas North African and South Pacific cultures associate green with corruption and danger respectively.

For more information on color meaning by culture, try a site like ColorMatters. There’s a lot of resources that touch on this topic. We encourage you to leave comments on the post if you have other examples to share.

So, beyond the varying meanings from culture to culture, why else would the red-green color scale be less than optimal?

If you’ve studied visual perception and design, you’ve probably come across the subject of color blindness. Two common forms of color blindness, Deuteranope (aka  Green blindness) and Protanope (aka Red blindness), will essentially render the red-green color scale useless for those affected by either.  Below are examples of what these users would see:

Normal Vision:



Deuteranope (Green blindness):



Protanope (Red blindness):


Our suggestion: use an orange-blue scale. While the colors will still appear different to the color blind, the hues will still provide enough differentiation for analysis. It may take some explanation up front, but consistency on this will lead to quicker processing.
 


Cheers,



Kevin A. Taylor 

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