@f_SI - The solution from @cmestry does NOT apply to Qualtrics and won’t record the answer to the NPS question. 

I just wanted to add that it is not advisable to use colors that suggest in any way that the rating was 'positive, negative, or intermediate”

@f_SI I would also suggest not to colour the NPS scale. 

It is not intended to be and if you need to do this, then you are using the incorrect metric. 

Unfortunately when others do this, it making it difficult for others who seek to use NPS appropriately.  You would be better using a simpler scale/metric which doesn’t need to ‘educate’ the respondent to respond the way you want.