@Katie_W Please use the below custom code. You just need to add '!important’. The !important rule in CSS is used to add more importance to a property/value than normal.

.Skin .QuestionText
 {
 color: red;!important
  }
.Skin .QuestionBody 
{
 color: red;!important
}

Thanks for your reply. This still hasn’t worked - is there anything else I can try?

Thank you

@Katie_W I am hoping that you are using the code under the Look and Feel as per below SS.

Yes, I have put it in the ‘Custom CSS’ box under the ‘Look and Feel’ tab

I wondered if anyone else has any suggestions for what to try here? Thank you

Hi @Shobhit 

The code provided by @Katie_W should work but still you are facing issues, try identifying the elements of that part of the survey which is still unchanged and then add them in the same code provided. Please see below code for your reference.
 

.Skin .QuestionText
 {
 color: black;!important
  }
.Skin .QuestionBody 
{
 color: black;!important
}

.Skin .QuestionOuter 
{
color: black !important;
}

.Skin .Matrix table td,
.Skin .Matrix table th {
    color: black !important;
}
.Skin .EndOfSurvey,
.Skin .Q_lang {
    color: black !important;
}

Here, Matrix refers to the matrix question and similarly the End of Survey message that I have in my survey. 
Hope it helps!

This code worked for me