VM has install VMware tools, why the value of guestHeartbeatStatus read by vSphere sdk is gray

[luna2019]

1. guestHeartbeatStatus is a filed of VirtualMachine, the enum values as below:

guestHeartbeatStatus

ManagedEntityStatus

The guest heartbeat. The heartbeat status is classified as: gray - VMware Tools are not installed or not running. red - No heartbeat. Guest operating system may have stopped responding. yellow - Intermittent heartbeat. May be due to guest load. green - Guest operating system is responding normally. The guest heartbeat is a statistics metric. Alarms can be configured on this metric to trigger emails or other actions.

2. vSphere client veresion is 6.0.0 build 3617395

GUI shows VMware tools running, why the value of guestHeartbeatStatus is gray, Theoretically it should be green, or there is anything which is forgotten to config?