Rumor has it that the iPhone 5S home button is going to be ringed in silver. According to Clayton Morris who told this week in tech, that he was sure about the change and that the button would otherwise have the same concave design.
The most solid evidence would probably be in Apple's media event invitation for the September 10 announcement. In addition to colorful circles, the empty silver rings could allude to a ring around the home button on the 5S.
Still a speculation, but don't be surprised if it really is true. [Apple Insider