The above and below pictures is shared by Hamza on his Twitter account which shows configuration options in a hidden Settings panel, which could allow iPhone and iPad users to tweak the UI with different fonts and also change the text colors and highlights.
However, as developer Steve Stroughton-Smith points out it seems unlikely that Apple will provide this customization options to the end user, and could be useful to a developer to debug label and tint colors.
Developers can access these hidden customization options by enabling the UIUseAlternateUI global preference in the iOS 8 UI kit on their device.