It seems that Apple might be adding another colour option for the iPhone 6s, but Sapphire Glass might not be a feature.
Spigen, a well-known casemaker has a track record of producing cases that match the colour options of preexisting iPhones. It has recently started selling its cases for the upcoming new iPhones and has added rose gold as a colour option.
What's interesting is the cases have not increased in thickness. As Sapphire glass is slightly thicker, it would make sense that the cases would also have to accommodate that. As the cases have not changed in dimension, it could be assumed that the new iPhones havent changed either. But right now all that is conjecture until the phones are actually launched in a week.