How to change text color for generated form

My form was created via SharePoint Library. When the form is created in Nintex all the text is black. Most of the items I am able to double click and change the font color in the Control Settings. However, there are two Control Settings that do not have an option to update the color of my text and these are checkboxes. Instead I am seeing this (please see attachment). How do I change the color of the text if I do not have the option in the control setting? CSS? Where do I add it Control CSS Class or CSS Class?

Thanks!