Big thanks to Eric Sloof for this gem:
In Virtual Center the maps function allows me to see whether a Virtual Machine can be successfully moved between ESX hosts (Vmotion, for example).
The maps can show an entire infrastructure. All the relationships between the ESX servers, storage, Virtual Machines and virtual networking. As you can imagine, this can very quickly begin to resemble a plate of spaghetti with lines and icons all over the place.
Map views can be generated for individual machines making sense of chaos, as it were.
However, as Eric points out:
If one of your ESX servers is under a heavy load it’ll show a light green colour. On the other hand, when one of your ESX server is not CPU intensive at all, it will show up dark green.
http://www.ntpro.nl/blog/archives/803-A-whiter-shade-of-green.html