Color
Use Color-Blind Safe Palettes.
About 8% of men can't distinguish red from green. Design for them too.
Roughly 8% of men and 0.5% of women have some form of color vision deficiency, most commonly red-green. Pick palettes that remain distinguishable in CVD simulators (ColorBrewer, Okabe-Ito, viridis). Pair color with a second channel - shape, position, label - whenever the distinction matters.
Brewer, 1994 · ColorBrewer · Okabe & Ito, 2008