What is "indigos"

Usage examples of "indigos".

Sunlight streamed through the transparent webbing and was split into soft, shimmering azures and indigos and golds and greens that cycled through the spectrum, over and over, endlessly, like a Gregorian chant.

The evening light would concentrate itself into the band of sky over the black jagged peaks of the Hellespontus, brilliant pinks and silvers and violets shading up into dark indigos and bruised blacks, and their voices would soften in that last part of the twilight Michel called entre chien et loup.