The back feather has the added advantage of being a mottled brown. One of the most common uses of hen hackle is for dry fly wings. Everyone wants to tie an Adams with perfectly shaped grizzly hackle wings that are as beautiful as they are functional. Hen hackles are easily the best choice for dry fly wings. Most hen neck feathers have an obvious web line, which makes the wings more visible in the finished fly.
Necks also have a large range of feather sizes, allowing for wings on various sized dry flies.
Finally, a good hen neck will have hackles that have a fairly broad outline all the way to the tip with a rounded, rather than pointed, tip. If your intention is to purchase a hen neck for dry fly wings, you are well advised to purchase them in person so you can examine the shape of the feathers. If this is not an option, order from a trusted source and clearly explain that the neck will be used for dry fly wings. Ask your supplier if they have access to pullet capes. You won't be sorry.