Circles are about managing who you want to share content with, and who you want to see content from. Sharing via Circles is much closer to Twitter than Facebook, but still different enough that Circles should be approached as a completely new model for sharing content that extends beyond the virtual wall of the Google+ system. This is very important to understand. You can share with anyone, even if they don't have a Google+ account.
Blue Circles are the ones you can put people into.
You can create your own blue circles, to categorize relationships.
Putting someone in a blue circles means:
- I want this person to see what I share with this circle. Aka, Facebook and private Twitter accounts.
- I want to see content shared by this person. Aka, following someone on Twitter.
Posting to a Blue Circle means you want to actively share/push content with the people in that Circle.
- If they do have a Google+ account and you are in one of their circles, then your post will show up in their stream. Aka, Twitter and Facebook.
- If they do have a Google+ account and you are not in one of their Circles, then your post will show up in their "Incoming" feed. (Users can choose to include these types of posts in their regular stream as well.). Aka, Twitter @user mentions.
- If someone doesn't have a Google+ account, then they will get an email with the content (and an invite to the service, I think). Aka, email distribution lists.
Blue Circles enable sharing with people who are not on Google+.
Green Circles are meta circles for passive sharing.
You cannot create green circles.
Posting to the Green "Everyone on the web" is exactly like a Twitter post from an unlocked account.
- If someone has you in one of their Blue Circles, then they will see the post in their stream. Aka, being followed on Twitter.
- If someone from your Blue Circles does not also have you in one of their Blue Circles, then they will not see the post. Aka, Twitter (they are not following you back).
- If someone does not have a Google+ account, then they will not see the post.
Posting to the Green "Circles" or "Extended Circles" behaves like posting to "Everyone on the web" except to the appropriately restricted set of users.
There is no way to create Blue Circles for sets of users that you want to be able to passively (Green Circle behavior) share content with. If you think about Blue Circles as ACL lists for posts, or the way Facebook thinks about Friends, then this will be frustrating. If you think about Blue Circles as people you want to share (via push if necessary) content with, then this is really, really nice.