Why is this?

I took my ex off of everything including iMessage. We both have iPhones. I know I shouldn’t be doing this, but it’s showing his number as green and not blue. I told my sisters to type his number into iMessage and theirs shows blue. So, I’m confused why this happening? If he blocked me, it wouldn’t be green it would just say not delivered if I even tried to send a message. It’ll be 2 weeks of us being no contact. So why is this?