Text messaging SMS inconsistency

My phone keeps doing this weird thing where I will message someone with an iPhone and it sends as a SMS. For example, my best friend has an iPhone. I'll message her a couple of times in a row and usually the first text shows up as green then the rest send as blue. It has been doing this for a week or so, I've restarted my iPhone, adjusted the settings and turned on/off SMS and send/receive settings. attached is a picture I tried looking for Messages in my cellular data setting but I couldn't find it. Also, i've been sending texts on both wifi and lte and this has still happened. It's not just with one of my contacts either, it's almost all of them that I have communicated with in the past week