Returns the atlas palette when it can tell the atlas's regions apart, and
otherwise a palette of automatically assigned, distinguishable colours. Use
this instead of reading atlas$palette directly whenever the palette is
about to be drawn: some atlases are built from colour lookup tables that give
every region the same colour (often black), and rendering those faithfully
produces a solid silhouette in which no region can be told from its
neighbours.
Details
A palette is treated as unusable when every one of the atlas's regions
resolves to a single colour. Contextual geometry – the cortex_ silhouette
and the unknown medial wall – is excluded from that judgement and keeps
its conventional grey in the fallback, so backdrop is never mistaken for a
parcel. Atlases with a single region, and palettes that are merely dark but
varied, are left untouched: this replaces palettes that cannot be read, not
palettes that are unusual.
Falling back warns, naming the atlas, because the fix belongs in the atlas's colour lookup table. An atlas carrying no palette at all is a supported, expected state rather than a broken table, so it falls back silently.
See also
atlas_palette() for the palette exactly as stored.
Examples
# A well-formed palette comes back untouched
identical(atlas_plot_palette(dk()), atlas_palette(dk()))
#> [1] TRUE