What is the meaning of the colors of parts in the Progress app?

In this example the parts and learning objectives have a blue color. This means that one or more students are working on these parts or the associated learning objectives. On the spheres of the parts a number is displayed. This number indicates how many students are active in this part. In this example, 4 students are active in part 1 and 2 students are active in part 2. If the spheres are grey, like the spheres of part 3 and 4, there are no active students for that part.

The small grey balls indicate where the students are active at the moment.