For all of you that do not want to use the new theme, i've added support to configure the theme via environment variable in 3.0.76. Add OMV_WEBUI_THEME=(triton|gray) to /etc/default/openmediavault to switch the default theme. After that you need to remove the cache files in /var/cache/openmediavault/cache*.json.
Tip: you can do it from shell: only need to type:
2017.12.18: actually this do not work for OMV4, see: New OMV UI