Emphasize is a new jailbreak tweak for iOS 7 by iOS developer Ryan Petrich that enables iPhone users to select from a list of custom color schemes: Orange, Chocolate, Chameleon, Sky Blue, Plum, Scarlet Red, Viridian, Olive, Steel, Sienna, Watercolor and Hot Pink. Each theme is configured through the Emphasize menu in the Settings app, and can be applied systemwide or to individual apps.
Petrich has been leading the pack with updated tweaks for the iOS 7 jailbreak, most recently previewing both FlipControlCenter and Display Recorder. He is perhaps best known as the creator of Activator, a useful iOS extension that enables certain multitouch gestures to carry out an action or shortcut. Activator relies on Mobile Substrate, which also require an update for iOS 7.
Emphasize is available on Cydia as a free download by adding the repository rpetri.ch/repo to your sources. While I can confirm that the tweak functions without issues on an iPhone 5 running iOS 7.0.4, your experience on a 64-bit device like an iPhone 5s might be different. Let us know if it works for you in the comments.