Gray, Silver and Gold were the colors of iPhone 5s and 6. With iPhone 6s and 6s+, Apple is going to bring in a new color in the form of rose gold. It is basically a mix of pink and gold color. Girls would like this color a lot. Apple wants to improve the number of women buyers of iPhones. Hence, they have decided to bring in this new color for iPhone 6s and iPhone 6s plus.
Gold color already exists in iPhones. Rose gold would be nothing but a pinkish variation of gold appealing to the sensibilities of women. Rose gold iPhone 6s plus would be made using anodized aluminum material unlike other colors. ion-X glass would be used for the display screen of iPhone 6s plus. ion-X glass is the term coined by Apple to refer to ionized glass. Apple seems to have done away with sapphire crystal for this particular color while they continue to use it for other colors.