On Android 4.4 KitKat you can set the Status and Navigation bars transparent with the android:windowTranslucentStatus and android:windowTranslucentNavigat
To clarify @suckgamony's answer to this question:
android:statusBarColor or android:navigationBarColor to @android:color/transparent will make the Status Bar or Navigation Bar (respectively) completely transparent, unless:android:windowTranslucentStatus or android:windowTranslucentNavigation is set to true, in which case the Status Bar or Navigation Bar (respectively) is set to the solid transparent color @AxeEffect describes (again, under Lollipop and above);android:statusBarColor and android:navigationBarColor may only be used with Android version 21 (Lollipop 5.0) or higher. As described in the referred to answer, android:windowTranslucentStatus or android:windowTranslucentNavigation when used with Kitkat provide transparent gradients rather than full transparency.