It would seem that applying
any label color is the only way to change the text from white to black.
Sorry.
I'll try checking Tinkertool and/or OnyX later to see if they have any options that have 'hooks' to these OS settings. Apple is slowly changing where and who can access these OS settings and that means things we or a developer could change in the past can't be done in newer versions of the OS. Apple, of course, will claim this is for OS stability and who am I to argue. Certainly many 'hacks' had detrimental effects on earlier OS versions!