Discovered by Santosh from checklist Segmentation-Free Testing.
Tested on Mac OSX Moneterey Version 12.6.
Strictly speaking this has nothing to do with free testing segmentation per se.
I cannot reproduce the issue in Ubuntu 20.04, maybe it's Mac OS specific.
In the MITKWorkbench, Window->Preferences.
In the Preferences Window, Go to the General option in the left column and then "Theme". Switch the theme from Dark to Light.