It seems that the color on the CS is a coating on top, instead of being infused into the glass as previously, and thus that Apple has opted for a more shatter-resistant material at the cost of being more prone to scratches and marks.
Well my ceramic cooktop is infused black or at least has a black substrate that shows through, can take a beating from heavy pots and pans, and doesn't have a scratch on it after two years of use. If what you say is true, it seems like quite the terrible design choice. Paint your nearly indestructible CS in an area that will be magnetically attached to many hard objects, Apple's own MagSafe puck likely being one of them. Not to mention the heat wear from day to day charging. "Just slap a case on it" I hear people say but I've never needed to with my 15PM while charging and it's "inferior" tinted glass rear doesn't have a scratch on it. Speaking of, that's definitely the phone I'll be sticking with this year 👍