The RedGreen feedback cards are credited to Jerry Michalski, a consultant about social change and technology. Their instructions are:
Red/Green cards, designed by Jerry Michalski (image from Flikr)

Quote:
Ever wish you could talk back
to the speaker at a conference?
To offer approval
or register dismay?

Use RedGreen feedback cards.


Michalski later also described the yellow and grey cards as
  • Yellow - if they are neutral, but energized
  • a grey card with a big question mark on it, signifying "Huh?".

More recently, a red-green app was created for the iPhone. This simply shows a green screen when the phone is held one way, and red when rotated 90 degrees.



This feedback to the speaker and group has also been described as a back channel, providing information in addition to the speaker's forward channel.

Although the concept is simple, people in the meeting need to be aware of the meaning of the cards. Similar cards are used by other types of group meetings for other purposes. Some groups use red/green during voting. Some use green/yellow/red to warn a speaker how much time remains. Some use red/green as part of a demerit system. Some groups which are process-oriented use them to indicate when the meeting is proceeding properly or has gone off-track.