Why do my text bubbles sometimes change color on the same number?

I understand that it's blue when using iMessaging and texting between iproducts, and green for standard SMS messaging.
However, when I text a friend of mine with an iPhone, while most of the time the text shows up as blue, occasionally it shows up as green. Is there a reason for this?

Wi-Fi porpises

You don't understand

  • Why on my iphone does it sometimes show texts in green, and sometimes in red? I have a iphone 4s, my son has iphone 5. Sometimes when i text him, the text appears in green, and sometimes it appears in blue. Does anyone know why this is?
  • Why does my iphone sometimes connect to Itunes and sometimes can't? Sometimes i can connect my iphone to my computer and it says iphone apple device. But sometimes it says device unknown? Can anyone help on this? Also, my Itunes need to open so my iphone can connect. I don't know why.
  • Why are some of my text bubbles dark bule? I have just realized that some of my text to and from my husband are dark blue. He doesn't have a iPhone and he has a different phone carrier as well. Can anyone tell me why it's doing that?
  • Why am i getting text messages late sometimes? I have an Iphone 5c. And with this one girl i talk to often, this seems to happen and it's annoying. I'll text her back and forth, then one day ill text and it looks like she ignores me the entire day, until the next day. Just out of the blue in the afternoon all her responses to that LAST day (Where i was being supposed ignored) Just pop up on my phon efrom that day. Why does this happen?> is it my phone? Hers? Connection?