'rainbow') is a genus of small paravian theropod dinosaur from China that lived during the Late Jurassic period.

[1] At Gangou, Qinglong, in the north of Hebei province, peasant Yang Jun discovered in a quarry near the village of Nanshimenzi the skeleton of a small theropod, belonging to the Yanliao Biota.

[1] In 2018, the type species Caihong juji was named and described by Hu Dongyu, Julia A. Clarke, Chad M. Eliason, Qiu Rui, Li Quanguo, Matthew D. Shawke, Zhao Cuilin, Liliana D'Alba, Jiang Jinkai and Xu Xing.

The generic name is the Mandarin caihong, 彩虹, "rainbow", in reference to the splendor of the fossil and the spectrum of new scientific insights it offers.

[1] The holotype, housed at the Paleontological Museum of Liaoning with the accession number PMoL-B00175, was found in a layer of the Tiaojishan Formation dating to the Oxfordian, about 161 million years old.

[1] Besides, Caihong was especially distinguished from closely related genera of the Yanliao Biota, such as Eosinopteryx and Anchiornis, by the presence of prominent lacrimal crests, longer pennaceous feathers on the forelimbs and hindlimbs and tail feathers with large asymmetrical vanes.

In front of this orbit, the lacrimal bone has a long and robust horn-like process, oriented sideways at its base and gradually curving upwards at its tip.

The tooth row in the upper jaw is exceptionally long, reaching to a position below the front of the eye socket.

The transition to the middle tail, defined as the point behind which transverse processes are completely lacking, is between the seventh and eighth vertebra.

The ulna is longer than the upper arm, a trait which in theropods is generally limited to flying birds.

[1] In the pelvis, the blade of the ilium is long before the position of the hip joint, but short and slightly curved downwards behind it.

On the breast and limbs, four centimetres long feathers are visible with parallel straight and thick barbs.

[1] The fossilized feathers of Caihong possessed nanostructures which were analyzed and interpreted as melanosomes, showing similarity to organelles that produce a black iridescent color in extant birds.

However, these structures are seemingly solid and lack air bubbles, and thus are internally more akin to the melanosomes in trumpeters than hummingbirds.