IIRC, it's been a while since I've been in the T1 lounge, that it shows the second agent inside the F lounge that you've been admitted entrance at the front desk. I think ultimately the decision to allow access (when trying to get guests into the lounge) lies at the person at the main front desk.

Don't think the colour means anything other than they rotate them from day to day to stop someone who has used the F lounge once as a guest using it for a whole year!