The "Save page" in the toolbar (i.e. the one that opens the save dialog, not the one that finalizes the save) should be 'progressive' (see [style guide](https://tools.wmflabs.org/styleguide/desktop/section-2.html)). In current skins (e.g. Vector) 'progressive' is rendered as a blue background.
Basically, 'progressive' (blue) means you're continuing the process (e.g. opening a dialog), while 'constructive' (rendered as green in current skins) means you're finalizing the process and taking a non-negative action (e.g. saving a page).
We want to maintain this distinction in general, but it's particularly important here because it uses the same text for both.
I understand that VisualEditor is not actually using the mediawiki.ui modules, but my understanding is the general idea is to be consistent with style guide.