Green plumage is nearly always an optical trick. A layer of feather structure scatters blue light while an underlying yellow carotenoid absorbs the rest, and the eye reads the combination as green. Crush such a feather and the green disappears. Turacos are the exception: turacoverdin is a genuine green pigment, and the related turacin is a red one, both built around a porphyrin ring holding copper.
The uniqueness is not absolute. Turacin, the crimson, has never been found outside the turacos. Turacoverdin is less exclusive: spectrophotometric work has reported the same or a closely related green pigment in the northern jacana, the blood pheasant and the crested wood-partridge, so the green is rare rather than confined to one family.
The pigments were identified in the nineteenth century, when chemists found that red turaco wing feathers gave up colour to alkaline water. This produced the enduring claim that turaco colour washes out in the rain. It does not: the effect needs alkaline solution, not plain water. The great blue turaco carries little turacoverdin and is largely blue-grey, so the family's signature pigments show best in the smaller green species.