Darker and more muted than Indanthrone, Prussian, or any other single pigment blue, this deep moody blue is useful for shadows, night skies, and other dark blue use cases.
Indigo pigment (PB66) is fugitive and not usually used anymore (though MaimeriBlu, a single pigment line, still uses it, and Schmincke has it in the mix). Most indigos, like this Holbein, are mixes chiefly of phthalo blue and black.