Do not rely on color alone
Keep category names, direct labels, legends, shapes, or position available. A reader should not need to distinguish red from green to identify success and failure.
Use contrast for hierarchy
Most categorical comparisons need one primary color. Use a contrasting accent only for the category the narrative needs to highlight. Muted context plus one emphasis color is easier to interpret than many equally saturated colors.
Test the complete chart
Contrast applies to text, grid lines, labels, and marks against the background, not just palette swatches in isolation. Review the exported image at the size where it will actually appear.
Preserve consistency
If blue represents Product A in one chart, keep it blue throughout the report. Reassigning colors between panels forces readers to relearn the legend and can create false comparisons.