Is the Save overlay permanent white colored ?
Because on some color combinations, it changes and it's difficult to see it.
"Colors demo" is just showing what is most probable result after changing colors, but it sometimes change more than needed. It would be waste of time to spend there hours on fixing these cosmetic aspect that is not even available in theme.
Basically what you see orange will change color to yours when you change color from theme settings, if something is white or black, it's not going to change color.
What color works best with this theme in your opinion btw?
There is probably no "best color", all depends on your brand, logo, personal preference, kind of business, what ever you like or need...