Within every project, you'll find the "Progress" section with subcategories "Roadmap" and "Budget usage". This article explains the color coding used both in the roadmap and the budget usage for each project.
Red: The deadline has passed but the milestone hasn't been closed yet.
Blue: The deadline hasn't passed, and the milestone hasn't been closed yet.
Green: The milestone has been closed.
Blue: External costs added to the project. More information can be found here.
Green: Internal costs added via timetracking. More information can be found here.