I think I figured out what the problem with the colour scheme is.

It isn't clear what is chrome and what is content. On the old boards, beige was content and the background was chrome, but here it flows into each other.

On this very "create a discussion" page, there are hard lines around the body of the post, but there are also hard lines around the title, the markup, the forum location dropdown and the preview and four different background tints and the whole thing is inside another border, adding up to a ton of lines and tints of green, making it difficult to tell at a glance what part of the screen belongs to what part of the page. It looks like "Post Discussion" is part of "Add a poll", for instance.

Long threads with tons of replies have the same border spam thing going on, but at least you can focus on the poster's icons.

Also, "Share as a link" is clickable (and difficult to read due to bold smallcaps) but "Posting as XYZ" is not, even though it has the same colour.

On the left, the search field is much less obvious than the "Boards" button (at least it totally looks like one but it's actually a link) and also blends into the background. Below is an actual button, "Create a discussion", which is awkwardly smaller than "Boards" and looks like it is related to the Guidelines.

Tl;dr The forums are pretty, but do a poor job at suggesting a workflow and making UI elements stand out.