On the phone, apart from accessibility settings described elsewhere, the only appearance configuration should be setting the background pictures for the welcome screen and home screen.
In the “Background” panel, “Welcome screen” and “Home screen” should be thumbnails of the actual screens — complete with tint and infographic for the welcome screen, and Dash contents for the home screen. (This conveys whether, and if so how much, the current background makes each screen less readable.)
If “Different background for each” is set and you choose “Same background for both”, the most recently chosen background should immediately be copied to the other screen. Conversely, if “Same background for both” is set and you choose “Different background for each”, the least recently changed screen should return to its previously set background, if that background picture still exists on the device, even if it was last used as a background months ago. (This allows easy undo of syncing the backgrounds.) If that background picture no longer exists on the device, the screen should change to its default picture.
Whenever “Same background for both” is set, the welcome screen and home screen thumbnails combined should function as a single tappable button, navigating to a “Choose Background” screen. Whenever “Different backgrounds for each” is set, the thumbnails should function as two separate buttons, navigating to a “Welcome Screen” or “Home Screen” screen respectively.
Unresolved: Current design for the infographic is to be mutually exclusive with a background picture.
All three of those chooser screens should consist of an image content picker — with a special album “Ubuntu Art” included just in this case, for use as backgrounds and nowhere else.
Choosing any of the items should navigate to a screen of picture thumbnails, where the header is the name of the item.
Choosing a picture from “Ubuntu Art” should navigate to a “Preview” screen, because that art is already optimized for the screen size.
Choosing a picture from any other source should navigate to a “Choose Area” screen, where by default the picture is centered and scaled to the smallest size that fills the screen; the “Best Fit” button should return to this scale and position, and be insensitive whenever the picture is already at that scale and position. The standard gestures should zoom and pan the picture to choose the area. If you do nothing for five seconds, gesture arrows should pulse into view in the center of the screen, hinting at how to zoom the picture.
This “Preview” or “Choose Area” screen should be unique in that the top bar, header, and toolbar should all be semi-transparent, so that you can see what part of the background picture will be visible when those elements are not present.
Choosing “Set” should set the background(s), and then navigate back to the top-level “Background” screen, because its thumbnails display confirmation of what you’ve done.