I'm not sure exactly what you're asking, and I'm being blunt, not sarcastic, but the answer is simply because they always do... if you mean the charging cord and headphones, it is the Apple standard to be white.
Apple doesn't color coordinate the accessories (as far as charger/syncing cord/ear buds). These accessories tend to work across several Apple products (iPhone, iPad, & iPods)...imagine the color combos they would have to supply considering the iPods come in multiple colors....and then consider the possible need to provide the same color range in replacement accessories (or backups...whatever you want to call the items you can purchase individually). If it's really important for you have color matched accessories for your black iPhone there are 3rd party accessories that come in black...just depends on if you want to invest the extra money. I've never seen it as odd but then again I'm used to it lol. As far as the ear buds go...I think that has been one of the most recognizable iPhone accessory...which was also a risk...I remember NYC Transit authorities advising people to consider using non-Apple earbuds when using their devices on the trains so that thieves didn't have a clear indicator of what passengers had valuable Apple devices versus some lower end mp3 player.