Trying to change to another palette. Clicking on palette side button for either font colour or highlight colour to offer alternatives shows the full list including a custom .soc put in ~.config/libreoffice/4/user/config but click to change to another palette no longer has any effect.
Fresh TDF build 18.104.22.168 does not have this bug (nor the rpm flatpak package of the same build) but is currently not as responsive as 22.214.171.124. A partial workaround is to remove the standard.soc from ~/.config/libreoffice/4/user/config of LO 126.96.36.199 and replace with customized standard.soc.
LibreOffice Version: 188.8.131.52,
Build ID: 184.108.40.206-3.fc24,
filetype : .odt,
OS : Fedora 24