n. Blue dye obtained from India or produced synthetically. If you want to get really technical, indigo is the color on the spectrum between about 450 and 420 nm in wavelength, placing it between blue and violet. In fashion, usually used to describe color of denim.

Go indigo (and wide) in these Diane von Furstenberg Gavin Jeans in Indigo, on sale for $228 (originally $325).