Robert Simmon’s blog posting series / video “Subtleties of Color” presents a compact overview of the most important considerations when using color. He suggest sthat in the opening paragraph that folks choose colors from a “Drop down menu”, set “start and end points” and click apply. So Simmon is addressing a problem that many tools default to color palettes which are either inappropriate for data visualization or perhaps even well constructed palettes can be applied poorly.
Simmons proposes that the highest quality examples of color theory come from the world of cartography, a field with a long history that has had much opportunity for refinement over the years. It’s hard to argue with this, given that a data vis legend like Bertin was also a cartographer, and developed his system through his trade.
Simmon’s review of color theory, which in the video he remarks are just the very basics, emphasizes perceptual color spaces. His main point is that we need to design color palettes which are based on human perception abilities – not simply mathematical properties. For example, “lightness” (value) dominates human perception space, and we must consider this when choosing a palette. In the video this is clarified with the comment “There is no such thing as dark yellow” – meaning yellow as a hue choice may always be perceived as something bright.
Simmon also makes the point that essentially the task of choosing color for visualization is a mapping exercise. This is made very clear in a literal example with the Mars “sketch” and then later when items like divergent, sequential, and qualitative data. For example, it is useful to discuss “diverging data” before discussing “diverging palettes”. Identifying breakpoints in the data for example, is essential before mapping color to the data. For me, this highlights a limitation in a tool like Tableau – which encourages applying color palettes before really mapping the data.
I thought the example of using “categories” of color was useful (e.g. 3 shades of green for forest) is a helpful example. Also the examples using “natural” palettes vs. “unnatural” in the phytoplankton are helpful as well. The argument appears to be, create affordances that respect where the user is currently at - don’t over complicate the system if it will cause one to lose the audience. Hence this ties into the larger theme that proper color choice is one of “aesthetics and judgement”. I believe that actually most of these “judgement calls” could also likely be codified but that would be a large under-taking.