Overlays allow you to compare your current site conditions to any project plan. Choose the Overlay tab in the sidebar and select any layer from the list.
There is a number of things you can do with each overlay:
1. Adjust the transparency: the most transparent — to the left, the brightest option — to the right position of the slider.
2. The contextual menu on the right side of the sidebar allows for:
Edit the Title of the overlay
Edit the name of the overaly
Move the overlay into a different folder
Delete the overlay
You can also rename the overlay folders using the contextual menu of each folder as well as create new folders (groups) by clicking on the "Group" button on the top of the sidebar.
3. There is a slider control on the top of the sidebar to change the background color for the overlays: black, transparent, or white.