Right click on movie-window. Select "Subtitles" ... "Font" and select color (I would advise yellow or white).
I also advise to check (=select) "Save subtitle font settings" and "Use outline font" options, both at the "Subtitles"-tab of "Preferences"
Edited:
PS: Do
NOT double post; please remove your other post!
I've meanwhile removed my reply to it so that you can indeed do so!