Why do the indicators above doors stay gray in Portal 2?

I am playing Portal 2 CO-OP and have finished chapters 1 and 2. Above the doors (and in the pre-chamber) there are indicators. I think orange indicates if the chapter chamber number has been solved, but what does blue indicate? Something with the other player? Why does it stay gray? How to make it blue?

Or is it just something meaningless - because blue/orange is a theme across Portal series?

Based on this reddit thread, the bars indicate which chambers have been completed by the respective player. As each chambers are completed, the bars will be filled in.

• The blue bars indicate which chambers have been completed by the player controlling Atlas
• The orange bars indicate which chambers have been completed by the player controlling P-Body

In the first image, the player controlling Atlas still needs to complete Chambers 5 and 6 in the Team Building course.

In the second image, the player controlling Atlas still needs to complete Chamber 1 in the Mass and Velocity course.