Geom “ink”/“paper”/“accent” palette (ggplot2 4.0’s element_geom,
B2-7): recolours a geom’s built-in default colour without touching
every geom’s own color/fill field or needing a mapped/explicit colour
to be set first. None everywhere (the default) changes nothing —
byte-identical output. Marked #[non_exhaustive] so a later field can
be added without an ..Default::default() break.