Yes, I gave the steps in another post few days ago.
There are a few steps to import a theme. I guess since FMI deprecated the themes, they don't want to make it easy to import the old theme.
1. Create a new blank database in FMP15 (prior version) and named it ThemesFM15.
Note you can use a database that already has the theme that you want used on a layout, if so go to step 3.
2. Change the theme on the default layout to the theme you want. I used Forest.
3. Manage Theme and you will see Forest listed.
4. Click Duplicate.
5. Close file
6. Open your database with FM16, the file that you want the theme in.
7. Manage Theme
10. Select the ThemeFM15 from step 1 and you will see your custom theme Forest Copy.
11. Now you have Forest Copy under custom theme in your current database.
12. Rename to Forest. It will still show under custom themes
I stumbled around and discovered pretty much the same process.