To much of my surprise, these silicone cases are incredibly dirt resistant. I've said a lot about Apple's silicone cases actually in another thread here:
https://forums.macrumors.com/thread...-from-apple-for-mini-4.1923313/#post-22016254
And here are some photos of my wife's mini (sorry, somehow I can't post image addresses from my iCloud photo library):
https://www.icloud.com/sharedalbum/#B045n8hH4P53Ie
But to give you context, I owned the silicone case for my iPhone 6 for about half a year and it never once got dirty. Dirt just simply rubs right off. I marked it up with a pen from work (on accident, and not permanent!) and you can just wipe it right off with just your finger alone. Its completely
different from the bumper for iPhone 4/4s and the leather cases that started with the iPhone 5/5s. I've owned all of the Apple cases and those always got dirty over time (particularly the leather ones), unlike this silicone case.