The site design feature is not available on custom or legacy templates.
Why can't I use the site design features?
The site design features are available on select templates only
If you need help converting to one of the selected templates submit a ticket at firstname.lastname@example.org
Saved color settings do not transfer from one template to another
You can save a color theme. Once you switch templates Go to: Design>>Desktop>>Site Design
Click the Green Check Icon to activate a saved color theme.