Oppo
Custom Ringtone for Contact Groups auf Oppo
Oppo's Phone app plays one ringtone for every incoming call by default. That makes it hard to identify who is calling without looking at the screen first.
ColorOS handles group-specific ringtones inside the Contacts app rather than the Phone app itself. Each contact group you create can carry its own sound, independent of the general ringtone set in system settings.
Where to set it
Open the Contacts app, tap Menu ➔ My Groups, then select the group you want to customize. Open that group's Menu again, tap Ringtone, and pick the sound you want. The change only affects calls from members of that specific group.
Both built-in system tones and your own audio files work, as long as the files are stored where the ringtone picker can access them.
This setting only covers phone calls, not messages or app notifications, which use a separate notification-sound path. If a contact belongs to more than one group, keep memberships tidy, since overlapping groups can make it unclear which ringtone actually plays.
For a single important contact rather than a whole group, setting the ringtone directly on that contact's own profile page is quicker and does not require a group at all.