The black dots mean that the pool member/node is marked up by a monitor, but that the pool member/node has been disabled.
The black diamonds mean that the pool member/node is marked down by a monitor, but the pool member/node has also been disabled.
A black square means that there is no service checking on the pool member or the node, but the pool member/node has been disabled.
In all of these instances, the pool member must be enabled before it will function. The biggest difference between disabled and forced offline is that disabled will allow persistent connections to be sent to the pool member, while forced offline will prevent any connection that is not currently active from being sent to the pool member.
I hope that answers your question.