Two everyday compounds.
靛蓝 is 'indigo' (both the dye and the colour - interchangeable with
蓝靛 and
靛青).
靛 standalone names the colour, especially when listing rainbow bands. Cultural note: the chengyu
青出于蓝 ('blue comes from indigo and is bluer than indigo') describes a student surpassing their teacher - the blue dye is
靛, extracted from the indigo plant
蓝.