When a custom field with radio options is created it has sometimes a clear option (see below)..
And sometimes it's not available like the color field. The first thought is that the reason is that the color field is mandatory, so the clear option is not needed, but that's is not the case. It is also optional. The missing clear option is annoying because it's not possible to undo a wrong choice. The used CiviCRM version is 5.28.