Hello. I just got a used white 4S from someone (had to come back from an SII) and there is black dirt in places. In places along the edges right between the glass and the (plastic?) space. And in between the home button. Is there a safe scratch free way to clean this dirt out? If I scrape in there with something, will the white plastic lose its paint? I'm hoping its dirt and not the plastic area with its paint lost. Thanks.