We have a pretty official answer
The Q&A with the Warhammer team was released today and they actually answered a question that I submitted! Whether or not I was the only one to ask I don't know but I wanted to clear up the vanguard and sternguard bone or green debate. The one host said that going off of lore that sternguard and vanguard would be painted bone since they are indeed deathwing. However, he acknowledges that there is a case for the painting them dark green especially if they are a part of the third, fourth, or fifth company. He did say if they are veterans of these companies they generally wouldn't have terminator honors, so maybe of you do paint the green change out their shoulder pad with the crux terminatus to a regular one. He also said at the end that to paint them the way you want which I totally agree with, I just know that there are some of us like myself who like to be as lore accurate as possible.
Link to Q&A : https://youtu.be/QEJQomLZy68?si=sBQ6r0SWAmYBJLZ8 Question begins at 29:16