Feather color accounts for most of the variation that we see in the appearance of birds, since color fluctuates with age, sex, and other factors, but a bird’s appearance can also change dramatically based on how the feathers are arranged.
Willet provides an obvious example. Its white wing stripe is invisible when the wings are folded, but striking when they are spread. Other examples include the red crown of Ruby-crowned Kinglet and the wing patches of Red-winged Blackbird. They, too, can be hidden entirely beneath other feathers and then dramatically revealed during displays.