These are status indicators passed through the vmware probe coming directly from the ESX host and/or VCenter.
From the VMWare SDK?API:
The current status of the hardware
Green: The physical element is functioning as expected
Red: The physical element is failing. It is possible that some or all functionalities of this physical element is degraded or not working.
Unknown: The implementation cannot report on the current status of the physical element
Yellow: All functionality is available but some might be degraded.
Basically, it?s a general health status.? However, there does not appear to be any document that describes what conditions would make a CPU (for example) go from green to yellow, etc.
Further detail would need to come from VMWare support.