In addition to the previous answers, many colourful things in nature are the result of multiple pigments interacting, and sometime non-pigmented colour with pigments, two create the final appearance of colour we see. There are several different chlorophyll pigments responsible for the green of plants (granted, most of them are in various greens) while there is no green or blue pigment to be found in birds, or indeed most other animals. Green feathers utilise yellow pigments, and stacks of microstructures that refract light between them until they emerge as blue iridescence.
Note also that other species see more, fewer, or difference colours in the light spectrum, and not all colours and patterns are meant for or possible to see seen by our eyes.
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