Every new version of Android offers a tweaked graphical style. KitKat’s UI differs a bit from the more prominent Holo blue from Ice Cream Sandwich and Jelly Bean, as that blue color was replaced by aesthetically appealing white. Unfortunately, some elements still appear to be taken directly from Jelly Bean, which is most likely true.
If you’ve ever wondered how “proper” KitKat should look, you should take a look at the guide presented by XDA Senior Member enricocid, who made a KitKat look more KitKat-like. Enricocid used some values from the SlimROMs repositories and shared the smali code, which can be used to complete the look of KitKat. Many elements were changed, such as the buttons, progress bars, page indicators, and more. More screenshots with applied changes can be found in the thread.
If you own a Nexus 4, 5, or 7 and don’t want to look deep inside into smali code, you can easily download a ready-to-use modifications that can be applied in the recovery. But if you want to play with smali code, don’t forget to download some tool to recompile the application, and of course make sure that your device is rooted.