Apple has always tried to worship the dual deities of clean design and usability - and while those two often complement each other, sometimes they butt heads. Case in point: iOS 7.1 changed the color scheme of the shift key so that users just can't tell whether it's on or off. It blends in with function keys when it's off, and with the letter keys when it's on, but neither color intuitively suggests an "active" state. Allen Pike points out that making it stand out in any way would easily solve the problem, but standing out seems to be against Apple's dogma of clean design. A fix may be in the works, but in the meantime its aesthetics 1, usability 0.
[Thanks to Jonathan Jackson for the tip on this one!]