The selected overlay defines what information is shown on top of the layout. You can switch to see the room layout in another overlay by selecting another overlay tab at the bottom of the room layout pane. In Window > Show Overlays, you can define which overlay tabs to enable.
The Colo overlay of the data center shows you information on space and rack count. The color highlights will give you an insight to whether a rack or a floor space is open, reserved, closed or for internal use.
Open: the rack is empty
Reserved: the rack is reserved for a customer, but the customer is not using it yet. To reserve a rack go to the Planning tab, right-click the rack, select Customer and Reserved for potential customer
Closed: a customer is using the rack
Internal: the rack is booked for internal use. In the Planning tab, right-click the rack and select Properties > Customer. The customer is an internal user.
Open: the available amount of your sellable space
Reserved: the reserved amount of your sellable space
Closed: the used amount of your sellable space
Internal: the amount of your sellable space that is for internal use
Room Area: the area of the room
Sellable Space: the sum of your open, reserved and closed space. Your internal space is not sellable and therefore not a part of the calculation.
Space Efficiency: the ratio between your room area and your sellable space.