Colour: a judge with a black robe.
Aim: this hat points out the weaknesses in the idea. Criticisms should be noted and expressed only under this hat. This hat is the basis for Western thinking and therefore there is the likelihood that it can be over-used: its much easier to be critical than constructive i.e. it can be habitual.
It can be used to uncover why some ideas will not work.
What is wrong?
What will not work?
What are the problems?
What are the obstacles?
What are the risks?
What is the worst case scenario?