OneNote 2010's navigation bar draws each notebook's icon in the colour
Notebook Properties picks. The notebook glyph's cover now paints in its
tint, shaded over it, and every place that draws a particular notebook
passes its colour: the sidebar's rows, the notebook button (the notebook
shown), the palette, Move's destinations and the sync popup. A notebook
without a colour, and Open Existing, keep the glyph's orange. A notebook
in iCloud Drive shows its tinted book with a small cloud at the corner
instead of the plain cloud. ui's Spec gains `tint`, an icon colour apart
from the label's.

Notebook Properties' colour menu shows a swatch of each colour.

iOS reads the colour with sb_library_color and tints the list's book.

Assisted-by: claude-opus-5.5