The Xiaomi Mi CC9 and CC9e come in three different colors: White, Blue and Black. The Black is pretty standard, but the other two have special finishes on the back to create an iridescent effect (White) and an S-shaped reflection (Blue). Here's how these came to be. The diffraction grating on the Mi CC9 • Compared to the Mi 9 Diffraction grating is used to achieve the rainbow colors of the White models. The Mi 9 had a similar gradient effect on its back created by ridges etched into the glass, but those were one dimensional. The CC9 back is etched in two directions, which...
Source: https://www.gsmarena.com/a_closer_look_at_how_xiaomicreated_the_iridescent_backs_of_themi_cc9_and_cc9e-news-37944.php
