So, in order to populate Alt-1 through Alt-10 with the colours and images set up for the demo, I selected Theme Options > Import/Export, selected Import from file and then pasted the contents of dante_theme-options.txt from the Demo Content folder into the text box.
Be warned, however, that this import will wipe out all your current Theme settings so if you have already begun customizing, you probably want to do this on a separate test site.
For anyone who needs the values for Alt-10, they are:
Alt-10 Background Color: #1dc6df
Alt-10 Foreground Color: #ffffff
Alt-10 Background Image: none
Alt-10 Background Size: auto