If you own an Oppo phone, the software you use on it is called Color OS. This is an Android “skin” — proprietary software customization that goes over stock Android. Oppo’s software also appears on Chinese OnePlus phones (Oppo and OnePlus are sister brands under the BBK banner). Previously, it appeared on Realme phones, too, but those phones now have Realme UI.
See also: A dive into Oppo’s Color OS 12