Login box in branding configuration is white by default, and hardcoded that way.
An option exists but was removed with
NXS-3667 due to a platform bug.
Now that the bug is fixed with
NXP-24873 , the option should be available again.
Workaround is to add these lines to a XML extension
- In the Nuxeo Studio branding, the option is exposed for the background color of the login box
- The field is available for TP 8.10 +