Color makes some birds stand out and helps to hide other birds.
Though there are a great many things in nature that we can explain, we can only guess why some things are as they are.
One idea – and there are many exceptions – is that birds with brighter colors spend most of their time in place where their bright colors make them stand out, so they can easily be seen by other birds of their own kind.
Birds with duller colors live mostly on or near the ground. Their dull-colored feathers match the grass and leaves of their surroundings and make them hard to see. This protects them from enemies.
This may also be why nature gave the duller colors to most female birds. Since she must sit on the nest to hatch the eggs, the mother bird must be better hidden.
A male bird may court his mate by singing and displaying his flashing colors, in order to persuade the quiet little female that he is the finest bird in the world.
During the nesting time, he perches on a limb some distance from the nest. With his bright colors, he draws all the attention to himself, and away from the nest and young ones. – Dick Rogers