Data Visualization that Is Colorblind-Friendly — Excel 2007?
By Tim Wilson on in Data Visualization, Excel with 10 Comments
Wow. This post started out not as a post, but as what I thought was going to be a 5-minute exercise with Google to download a colorblind-friendly palette for Excel charts. That was two weeks ago, and this post is just scratching the surface.
Several weeks ago, one of the presenters in a meeting showed some data as a map overlay. As soon as she projected the first map, someone in the meeting quipped, “Good luck understanding this one, Jim!” Jim, you see, is colorblind. And, apparently, most of the people in the meeting knew it. Approximately 8% of men have some form of color blindness (it’s much more rare in women — only 1 in 200). And the overlays on the map were color-coded very subtly. Jim commented that it was hopeless!
As it happened, I was exploring a fresh set of data that same week, as we’d recently rolled out some new customer data capture capabilities. As I worked through how best to present the results, I decided to grab a colorblind-friendly palette from the web and use it in the visualization of the information. I’d hoped to find a site with one or more Excel files that I could download with such a palette, but, worst case, I was prepared to snag a palette and manually update my Excel file (for future sharing on this blog, of course!).
No. Such. Luck!
What I did find was a slew of information on the different types of color blindness (which I’ll touch on briefly in a bit), as well as a bevy of almost-useful tools and palettes:
- How to make figures and presentations that are friendly to Colorblind people — ultimately, I used the palette that is ~2/3 of the way down this page for my spreadsheet (the figure labeled “Set of colors that is unambiguous both to colorblinds and non-colorblinds”). Mr. Excel actually references this palette and provides a macro that will update a workbook’s palette with this palette. The downside of this palette is that, while it may be plenty functional, I can’t say I’m wild about it from an aesthetic viewpoint. But, I’d spent the 30 minutes I’d given myself to dig, so I ran with it.
- Colorjack Color Blindness Simulation — a view of the color spectrum as seen by people with eight different forms of color blindness. That’s informative…but doesn’t really provide a realistic way to build a functional palette for data visualization purposes.
- Colorjack — a nifty tool for finding a color palette. Unfortunately…there’s no way to test how colorblind-friendly any of the palettes are
- Colorblind Web Page Filter — there were a number of tools for sale that would simulate how content would appear to people with different forms of colorblindness, but this is the (free) online tool I wound up using for the exercise below. It couldn’t be easier to use — you just provide a URL and what form of color blindness you’re interested in, and it renders it
So, aside from the one palette that was solely focussed on functionality and not at all on aesthetics, I struck out. As I pondered this over the next few days, it occurred to me that, perhaps Excel’s default colors always seemed so gosh-awful because they were actually developed explicitly with colorblindness in mind. I could not find any documentation to support the theory…so I turned left and headed down that rathole to see if I could figure it out myself.
The exercise was pretty simple. I created a 10-color bar chart using the Excel 2007 default palette. Note: This was created purely for palette-testing — this actual chart is a great example of needlessly using more color than is needed! Here’s the chart:
Like the one colorblind-friendly palette I found online, I really don’t like the aesthetics of this palette. It’s been toned down a bit from the Excel 2003 (and earlier) versions, which is good, but it still seems rather harsh. Could that be for colorblind compatibility? I think so! I took the chart above and ran it through the Colorblind Web Page Filter mentioned above for the four most common types of color blindness (as described in a Pearson report by Betsy J. Case):
Overall, the palette seems workable in all four situations. The first three colors absolutely work. Color 4, as well as color 5, start to lose a little contrast from color 1, but they still seem manageable. Color 5 and color 7, as well as color 10, start to get a little problematic in some cases, but, if you’re going beyond four colors in a single chart, you might need to reconsider your chart type anyway. Right?
Now, one final test: for achromatopsia. On the one hand, this is extremely rare. On the other hand…it’s common when your office has a lot of black-and-white printers:
Apparently, any palette that works in grayscale is a quick way to check for compatibility with all forms of colorblindness. It’s also…a best practice. Interestingly, the Excel 2007 palette really lays an egg here, in that colors 1, 2, and 4 are all barely distinguishable!
Clearly, there is an opportunity here to test a variety of functional, attractive palettes for grayscale printability and the top four forms of colorblindness and develop something better than the Excel defaults. But, that’s an exercise for another time. I think I’ll aim for the first four colors of the palette being “highly distinguishable” in all scenarios and the next four being “functionally distinguishable.” What do you think? Would this be useful? What else should I take into consideration?