Color patterns serve as camouflage against predators for birds in their habitats, and by predators looking for a meal. As with fish, the top and bottom colors may be different to provide camouflage during flight.
But they also provide us with many uses. Feathers are both soft and excellent at trapping heat; thus, they are sometimes used in high-class bedding, especially pillows, blankets, and mattresses. They are also used as filling for winter clothing, such as quilted coats and sleeping bags. They've even been used for arrows, to decorate fishing lures and to make quill pens. And during the 18th, 19th, and even 20th Centuries a booming international trade developed in plumes/feathers to satisfy market demand in North America and Europe for extravagant head-dresses as adornment for fashionable women. Now we can even use them to keep our plants warm as shown in these pictures on my flickr page and even just for fun in our house as this suncatcher shows. (Who hasn't heard of the 'Red Hat Society'? This is my stained glass tribute to them.