As you may know, there is a global to test out what MediaWiki UI will look like when it is enabled site-wide. See https://www.mediawiki.org/wiki/Manual:$wgUseMediaWikiUIEverywhere
Unfortunately, you can't test it right now due to https://bugzilla.wikimedia.org/71595 , but the edit page currently looks like:
https://i.imgur.com/h4GTzUB.png
(Thanks to Quiddity for the screenshot).
I think the main button bar is too busy. Save page is fine; that color is semantically correct and it's the main action.
However, I suggest we consider making preview and/or show pages neutral (basically, that looks like a button, but is not colored in the current skin).
I'm interested in other suggestions. See https://tools.wmflabs.org/styleguide/desktop/index.html for the features MW UI currently has.
Matt Flaschen