How do I know if I have been blocked

You are not blocking, but you may be being blocked by the other person. You cannot know for sure though.

It's also possible that they have not seen your message, of they have seen it but have not yet replied.

If you never get a reply from the other person, you can assume that they have blocked you or are totally ignoring you......so pretty much the same thing.

There is no way to know if someone blocked you. That's a personal choice they have and it's never shared with with anyone. The difference between blue bubble and green is nothing more than blue is iMessage, meaning iPhone to iPhone and green is SMS, meaning sent via your carrier.