iMessages stay green

I found no real answer to this question. This has only happened with the past two updates. if I send an imessage when my boyfriend has his phone off, they eventually go to green. It does NOT change back when he turns his phone off. I even reboot my phone and it is still green. It takes him sending me a message before it will go back to iMessages in blue. I think this is dumb. It’s annoying and I wish Apple would make it stop. I would rather know it can’t be delivered than to go to green where I have no clue if it was. It should not take the other person sending a message to reset it back to blue.