Every activity that a student completes on CodeHS (ex. videos, quizzes, sample programs and programming exercises) are color coded depending on their status.
Green: This exercise is correct and has been passed
Yellow: This exercise has been submitted by the student but is awaiting grading and feedback from me as the teacher
Blue: This exercise has been graded as "Functionality Ok", which means that while the student has technically completed the assignment or the goal of the exercise, there are improvements that can be made to the program (functionally or stylistically)
Red: This exercise is incorrect and will need to be revisited by the student
Student exercise submissions can be graded from the "Submissions/Questions" link on the top navbar of your teacher page. From that page you will find different tools that you can use to efficiently grade student work.
It is important to note that the first 5 lessons of "Introduction to Programming with Karel" are all autograded, so student exercises will go straight to Green/Passed. Once students reach "The Two Towers" in lesson 6, exercises will start being submitted to your grading queue (and will turn yellow).