I don't have duo or allo or anything like that on my Android phone, but I have one friend that I get different background color - a darker blue than normal sms,

I don't have duo or allo or anything like that on my Android phone, but I have one friend that I get different background color - a darker blue than normal sms, read receipts, and encryption, in the Google Android "Messages" app. We've never really dug in to why, as we're both using the default app. No other conversation has ever had this blue message and lock symbol and checkmarks going on.