Peregrine falcons have blue feathers atop their heads and on their backs. Males tend to be more brightly colored than females, so if you've seen one with a more grayish-blue coloring, it could have been a sex difference.

And yes, aeronautic design borrows a lot from birds. 😅

(Also, a peregrine's nose connects around to the back of its head. It breathes in through the front and out through the back. Like a turbine.)