I was thinking about this a little more from a software development perspective after our email conversation the other day.
I think the main problem lies in identifying the action to check for to trigger the color change.
When a guest volunteers, the action is discrete and can be "noticed" as a change in the state of the profile; however, there is no action to check for if a Greeter goes to visit a profile.
Even if they post a message there, you wouldn't want to change the status of the profile in the database because anyone can post a message on a profile, and it doesn't necessarily mean they've been properly greeted.
I appreciate your creativity and desire to make things easier, but for now, at least, I think the solution of posting the last line you worked on will really help.
Let's try that for a while and see how we do! :-)