For end users belonging to a company which has a theme defined, they still see the system default theme, although their theme picker depicts the company record's selection. 

1. Go to User Organization > Companies
2. Open a company (ex: Apple)
3. Configure form layout to add 'theme' field.
4. Select the 'rose' theme and save
5. Create 2 users (ex: Steve Jobs, Bill Gates)
6. Impersonate user (ex: Steve Jobs)
7. Observe the theme is still system theme
8. Use cog wheel and select theme section and notice that 'Rose' is selected.

Expected:
Per the official documentation, "In UI16, the basic configuration is used instead of the theme selected in the company record."

Actual:
Although the basic configuration is displayed, the cog wheel setting indicates the user has selected "Rose" - Selecting "Rose" then does update the theme.

This issue is under review. To receive notifications when more information is available, subscribe to this Known Error article by clicking the Subscribe button at the top right of the article. If you are able to upgrade, review the Fixed In field to determine whether any versions have a permanent fix.