ColorOS

ColorOS is a user interface created by Oppo based on the Android Open Source Project. Initially, Realme phones used ColorOS until it was replaced by Realme UI in 2020. Realme UI uses some of ColorOS's apps. Starting from the OnePlus 9 series, OnePlus will preinstall ColorOS on all smartphones that are sold in mainland China instead of HydrogenOS (Chinese version of OxygenOS).

The first version of ColorOS was launched in September 2013. Oppo had released plenty of Android smartphones before then. It was not stock Android, but Oppo did not label it as ColorOS. Over the years, Oppo launched new official versions of the operating system. To make things less confusing, in 2020 the company revealed that it would adopt the same numbering scheme as mainline Android, and as such, ColorOS jumped from ColorOS 7 to ColorOS 11 with the launch of Android 11.

It was announced that ColorOS, OnePlus' Oxygen OS, and Realme UI will merge to form a single Android skin that will appear on all OnePlus, Oppo and Realme UI phones. However these plans were cancelled as the three UI's are being developed on the same codebase, but they are separate.