Level 17 (black): only one stop or gym per cell. If grey background, there's already a portal there.
If yellow, someone has submitted a potential portal there recently (click an empty cell to add your own).
Level 14 (green): new gyms for the 2nd, 6th, and 20th stops.
The map is on break because of a change from Niantic that broke the software. Hopefully we'll be back up and running soon!