Apple tells developers that whether they're redesigning an existing app or creating a new one, they should consider approaching the job in the way that Apple approached the redesign of its built-in apps.
iOS embodies the following themes:
● Deference. The UI helps users understand and interact with the content, but never competes with it.
● Clarity. Text is legible at every size, icons are precise and lucid, adornments are subtle and appropriate.
● Depth. Visual layers and realistic motion impart vitality and heighten users' delight and understanding.