Categorical parsimony: use fewer colors
The most common dashboard color mistake is using a different color for every dimension in a chart by default. A bar chart showing revenue by month needs one color. A bar chart showing revenue vs expenses needs two colors. A scatter plot showing five product lines tracked across multiple charts needs five consistent colors — and no more, because human color discrimination in chart contexts breaks down after about seven distinct hues. Reach for lightness encoding (same hue, lighter/darker) before reaching for additional categorical colors.
