Font colour not changing in published quiz

Hello, 

I'm trying to customize the colour scheme for a quiz I'm making. When I preview the quiz in quizmaker the font colour is displayed exactly how I want it to be (dark grey), but when I publish the course, the font colour turns white (see attached screen shots). The font colour I'm trying to change is for the invalid answer feedback boxes (e.g. when the user doesn't select an answer choice and presses submit). 

Perhaps I'm not selecting the right text option for changing colours? It's hard to tell seeing is how the preview for the player template doesn't show the invalid answer box when trying to change colours.

Thanks,