I want to add ' Mark for review option ' in a Online Exam Project

Question

I am creating a website of online test in which a group of button with text 1 to 200. when candidate attempt the ques then button color will change to green . when candidate leave the ques ques then button color change red and a mark for review option for future review of ques and button color change purple when candidate mark for review. Now i want purple color retain throughout the entire test time untill candidate unmark . How will i get this? Plz Help