And all the people D1 folks gave positive trust to are then in D2 and so forth.
No. You have to be included in their trust list (
https://bitcointalk.org/index.php?action=trust).
Whether or not you have received feedback from any D1 user does not matter.
D1 is all the people Theymos trusts, if I'm not mistaken.
Default trust depth 1 are all those people in the trustlist of the forum account DefaultTrust (including theymos).
You're right as far as theymos is (one of the users) managing this list (
https://bitcointalk.org/index.php?action=profile;u=122551).
I got green trust because Vod very kindly gave me one, and he is in D2. So basically I'm in D3 (I think)
No.
How does a member get a d1 trust rating. I see that a lot of member have green true but only a few have d1 trust rating.
The vanilla setting for depth is 2, hence feedbacks from users on default trust (depth) 1 and default trust (depth) 2 show up as trusted and influence scores.