ok, jailbreaking allows the iphone to run apps that have not been signed for it, or to give access to the file system which users generally do not have access to, in order to modify files (which is what you want to do)
to change the colour, you need to hack the phone
each time there is a update (such as 2.0.1) a new jailbreak must be done, and there is always the possibility that you brick (break) the phone
it is easy - if you know what you are doing
if you do not (and no offence, you don't with regards to hacking the iphone) it would be easier to simply leave it as it is and accept the colours