What app has purple messages?

I saw my husband messaging someone and the message bubbles were purple. He exited out of it quickly when i walked in the room but I’m trying to think what app that might be? Anyone know?

Just asking a question not asking for relationship advice.

Update: he has messenger, I went through his phone and I think it was that. There were not recent messages so im assuming he deleted them but I asked him about it and he “doesn’t know what I’m talking about”