I like the color blue for no other reason than it looks the coolest to me. Blue is probably one of the rarest colors that one can find in nature apart from seeing it in the sky or seeing it reflected by the oceans. Peacocks have a bright green and blue plumage, which can be attributed to its structure rather than pigmentation. The blue morpho butterfly has the same situation in which its wing scales have ridges that refract sunlight so that they appear blue in our eyes. The same goes for the blue jay and even plants such as bluebells, hydrangeas, and morning glories, which all use pigments and the reflection of natural light to appear blue.
In the case of bowerbirds, they make their bowers out of sticks and brightly-colored objects, most of which are in a shade of blue, all for the purpose of attracting a potential mate. Why the bowerbirds have chosen this specific color, we cannot say for certain except for that, just like me, and many other people in the world, they simply like it. This phenomenon has also been documented by Charles Darwin in his book The Descent of Man. The Marginalian offers this interesting perspective on the bowerbird and the color blue in this article.
(Image credit: Joseph C Boone/Wikimedia Commons)