• All chats sets the background of every conversation that doesn't have its own.
• This chat gives one conversation its own background, for example a photo you took together.
• To make a chat follow the shared background again, open ⋯ → Chat background in that chat and click Same as all chats.

Only you see your backgrounds. The people you talk to keep their own.

Your choice is saved with your Narendi account, so it follows you everywhere: every browser where you use Wiply and the Narendi app. In the app, the palette button at the top of a chat opens the same background picker.