Unfortunately it's not.
You need to go to the community page and click on the "write a post" blue button on the top right corner and then create the post.
Another alternative is to click on the little pencil to create a post and then on the top left corner click the arrow in front of the "Write a new post in My Blog" and select the black and white community there. I am not 100% sure but I think this second option only works if you previously subscribed to the community.