Humans often use a metaphor to describe activated communication as a heat. We focused on this metaphor and developed an estimation model for activated interaction and communication by regarding an interactive communication space as a heat conduction in a virtual temperature space. In addition, we developed a communication system that changes the background color based on the model. This system supports sharing an interactive atmosphere even in spatially separated online communication by changing the background color from the black to the warm color. However, when the background color suddenly changes from the warm color to the black, it brings a negative impression of the silence of the conversation. In this study, we developed a new method that expresses the afterglow of the interaction atmosphere in the system. This method generates slowly changing the background color from the warm color to the black when the conversation is finished.