Meaning of colors (Mircophone Icon)

Hi,

I tried to find out the meaning of the microphone colors in Adobe Acrobat Connect Professional. As you can see in this TinyPic-Link, the mircophone icon changed his color temporarily from grey to yellow, not to green when users are talking.

Means this that the bandwidth is too low or that the cpu is too slow?

Thank for your help!

Best regards,
Alex.