I now understand the problem - the link to the latest version 25.09 for MacOS installs 25.07 NOT 25.09 even though the filename says 25.09. If, however, you then upgrade from within 25.07 to 25.09 using the Tools>Upgrade launcher then 25.09 installs and the custom colors are now sticky - thanks for the fix but please update the initial download link to avoid confusion!