With the changes to the theme guidelines where we have not allowed curve variation/clone themes into the mod site, I'd like to take a second to give a quick clarification on this rule.
The purpose we made this rule is because of the script in this topic
that allows you to make curve color variations.
So in essence, if you can make the theme with the script in that topic or if you create an identical theme with just color gradients, it won't be allowed on the customize site. If you customize your theme in a way that cannot be done with that script, feel free to submit it to the customization site.