If you're lucky enough to have an iOS developer account, then you had a brief glimpse of some of the darker options with the 7.1 update, including a darker keyboard. This was exclusive to developers who installed the first iOS 7.1 beta, but is no longer available, unfortunately.
For those of us that don't have an extra $100 to drop on a developer account, there is a way to get this dark keyboard, and not only as a preview, but as your default look. All you need is to jailbreak your iOS 7 device. Already jailbroken? Then this will be quick!
Step 1: Install Bloard
Open up Cydia... more