Solace Element Case for iPhone 6

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I recently purchased this case in blue for my fiance. First off, the case is beautiful and fits perfectly. But I've had one issue and I'm wondering if anyone else has had this problem. After just a few weeks of light use the case got surprisingly dirty. The edges have become noticeably discolored and we haven't found any good way to clean it. Nothing seems to get the grime off the case. I spoke with customer service (they were seriously fantastic) and they agreed to do a one time replacement, but they advised the issue could possibly happen again. I'm curious if anyone else has run into this problem. If so, were you able to clean it and what did you use to clean it? Thanks for any advice!