iMessages strictly work with data network. you seeing the blue and green randomly because you probably losing data network back and forth and for your husband, tell him to goto settings and check if his iMessages are turned on. Most Likely its turned off. Good Luck
I asked him about the setting earlier and he said it was on. I think the data network comment might be the issue. ATT, but using wifi while texting. Would that cause the issue? Being on wifi or is it ATT? Thanks!
if you are on wifi than you are good but if you are using ATT data than losing the data network will cause iMessages to stop working. On your husband iPhone, Goto Setting > iMessage > send and receive > click on apple ID > sign out and sign back in . This might work .