One teacher said, I do this in my gradebook - I get out some markers and color in whatever colors my students ended the day on. I use this to determine their citizenship "grades" for each report card. This one is CUTER, though!
This voice levels poster is used in most preschools during my placesment, I think it is an effective way for teachers to control the voices in the kinder. Child also remember the colors and related voice levels that they should use inside and outside.