In my other projects, the synopsis background was white independent of the label color of the document. With the new one, it’s not working that way.
Where do I find the option to change that (I can change it for composition mode, as above)?
Thanks.
At the same Appearance preference location then Index Cards > Colors > Index Card Background. And/or to remove the label color option—Scrivener menu bar > View > Use Label Color In > Index Cards.
There it is. Thanks, SC!
I sound like a broken record, but all preferences should be in one place or possibly one place for general preferences and one for project preferences. Rant over.
I wonder how that got changed? I opened an old project, saved it with a new name, then dragged and dropped some text documents over.
Not to worry! The grade earned for this find the Scrivener preference test is only 1% of your aggregate grade. 
[You’re welcome. Happy writing.]