Sounds like the Moon Butterfly Hat. Can't recall anything else that has some sort of feather attached to it that fits your description. There is also Lucatiel's Mask, but the feather looks rather black. Hmm... As for the Moon Butterfly Hat, the feathers (there are two) are yellow though, but they look a little reddish. Was there fur, too?
It's the falconer helm. Maughlin sells it. It's the matching helm to the knight class' starting armor (falconer set). --- http://tinyurl.com/c5ambvk - http://tinyurl.com/nrluepw - http://tinyurl.com/okfh7ba