I have the same question. The new 7.0 (Nougat). I notice this update is for "...improvements to your Galaxy S7..." but I have an S6 and I DO NOT LIKE IT!!! The issue I have with not being able to change the calendar default colors is I have several calendars synced to my phone, the ones I use the most are the "My Calendars" and my business email calendar, and this new update MADE THEM THE SAME COLOR!!!! UUUGGGHHHH!!!!!