I saw some references to YouTube Channels for someone named Abbie who does MAC themes, and there is a site with some nice free MAC themes as well. Except of course I’m running Windows.
One of the people out there in 'net world is willing to send me her hex codes, and in theory, I could use that to mark up an existing theme and save preferences (if I understood Jim’s teachings on another thread) that then could be loaded (instead of theme settings).
Is that the best way to start? Take one of the eight and tweak the colours? I would be willing to send the file back to the netizen if there was a way to share it afterwards. Just not sure which way to start – fresh and aiming to export a theme or tweaking and then expecting preferences?
I downloaded the MAC theme for one of them, and it was all in XML which I had momentarily hoped would be helpful as I thought the hex codes would be visible but the MAC stream is all hashcode. Sigh.
Paul
aka PolyWogg
Hi PollyWogg 
Windows themes are a combination of Preferences, a Palette, a Stylesheet and a XML-manifest, zipped in a .scrformat file.
You won’t be able to change a Theme updating File > Options > Appearance settings alone. Moreover the colors in the palette are used for several User Interface elements at the same time. The Stylesheet doesn’t cover all UI-elements, but enough of them create a good looking Theme. See Scrivener 3 Themes (Windows) for three complete themes (blue, green, brown).
Mac and Windows Themes are not compatible, as you’ve already discovered.
You can find hexadecimal color codes quickly with the windows color picker using the button Pick Screen Color. But a Theme comprises more than color codes.
The best way to start is to pick a Theme closest to the result your striving for, indeed.
Then you need to adapt that Theme file to your intended result.
Reaching a 100% pixel perfect result is probably unrealistic, but you can come a long way with some perseverance. 
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