I'm currently implementing the Google Visualization API into an existing platform, one requirement of which is the ability to choose custom colours for chart elements (such as pie slices and columns).
We will be producing pie charts, (optionally stacked) bar charts, (optionally stacked) column charts (and possibly scatterplots at some point in the future).
There is some consternation over whether to provide colour palettes as groups of similar colours to match the company branding (#138181) or to provide colour palettes of disparate colours such as those in the example links below.
I'm of the view that using disparate colours is easier to comprehend than similar colours, particularly when number of slices > 4. I have only ever seen similar colours used in the professional media when the maximum number of slices is around 5.
The kicker is that generated charts will have between 1 and 20 slices (pie slices, columns, or dot arrays in the case of scatterplots).
Answer
According to the principles of grouping, partly described by the Gestalt principle of Prägnanz, same-colored elements are grouped as a collective in the mind:
The law of similarity – The mind groups similar elements into collective entities or totalities. This similarity might depend on relationships of form, color, size, or brightness.
If the elements, in this case chart elements, are to be treated as differentiated entities, then you should use disparate colors. The only use where similar colors would be advisable would be if the chart elements had to be grouped when sharing similarities.
This is taken from an informational point of view. Other POV can be taken into account, as using similar colored elements for graphic design purposes.
Examples
This chart is a perfect example (never mind the labels). Green-hued pieces would represent a global similar attribute, in contrast with red-hued pieces (for example healthy vs. unhealthy types of food).
This is a common use of colors. Same-colored bars represent the same data at different times.
Here, the disparity of colors represents different type of elements, not to be grouped in any way.
Lastly, similar-colored elements can be used for aesthetic reasons.
As a bonus, I would recommend getting inspiration from Information is Beautiful's incredible charts (who, by the way, make a very good use of colors.)
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