Why is a black iPhone 4S is shown as white in iTunes?
iTunes deduces the color of the iPhone from the serial number he finds on the logic board.  For example:

MD269LL   = Black AT&amp;T 64GB 4S  
MD271LL   = White AT&amp;T 64GB 4S  
MD277LL/A = White Verizon 16GB 4S
...


So, check your model number and look it up to make sure you've got a black one.