Add custom text color to field in json



I would just like to be able to change the color of the words in the fields, for example, for the priority.
I would put red orange and green for the three states.
but I do not understand how to make this change in json.
I tried to change the “mypage.json” file ( picture in attached) that is generated for the language here:

someone can kindly help me to conclude this change correctly?
Many tnx!
Thanks a lot to everyone!